Access time. The amount of time it takes for information to be read from or written to a disk. The sum of search time plus seek time. ACID (atomicity, consistency, isolation, and durability). The four primary attributes ensured to any transaction by a transaction manager. Acronym. A word formed by taking the first letters or sounds of each word in a phrase and capitalizing them. For example, RAM (pronounced as a word) is an acronym for random-access memory. Address. A location in memory where data are stored and can be retrieved. Administrative strategies. Organizational policies and procedures for maintaining data integrity. After image. A copy of a record after a change has been made. It is used for forward recovery. Aggregate entity. An entity created from several entities having similar attributes often distinguished by a prefix or suffix. Aggregate function. A function, such as COUNT and SUM, that operates on multiple columns. Aggregation. A special version of an association relationship that reflects strong ties between objects. Alphanumeric. Data represented in both alphabetic (the letters A-Z) and numeric (the numbers 0-9) form. Alternate key. A candidate primary key that was not selected as the primary key. ALTER TABLE. An SQL command to add a column to an existing table or change the status of a referential integrity constraint. Anomaly. An undesirable result following update, insertion, or deletion of a record. ANSI. American National Standards Institute. Applet. A Java program that is downloaded into a browser and then run inside the browser’s window. Application development life cycle (ADLC). The stages of developing and maintaining an application. Application software. A computer program or set of programs intended to perform a specific function, such as accounting, payroll, word processing, spreadsheet calculating, or database management. Architecture. A term used by computer designers to designate the structure of complex information-processing systems. It includes the kinds of instructions and data used, the memory organization and addressing, and the methods by which the system is implemented. Archival file. A file kept as a permanent record. Arithmetic expression. An expression consisting of only numbers and operators, for example, 7 + 6. Artificial intelligence (AI). The branch of computer science that attempts to understand the nature of intelligence and produces new classes of intelligent machines. Areas of study include robotics, speech recognition, image recognition, natural-language processing, and expert systems. ASCII. An acronym for American Standard Code for Information Interchange. A seven- or eight-bit code that specifies a unique set of binary digits that represent a character set. Association. Links or connections between object occurrences. Associative entity. The by-product on an m:m relationship. It stores data about an m:m relationship. Attribute. A fact about an entity that becomes a column in a table. Authorization. Permission to take particular actions on a database (e.g., insert rows). AVG. An SQL built-in function for determining the average of the values in a numeric column.
B
Backing up.. Copying program or data files in case the original is lost or destroyed. Backup-file.. A copy of a file made for safekeeping in case the original is lost or damaged. Bandwidth. . The term used as a measure of the capacity of a communication channel expressed in bits per second. Base table. An autonomous, named table. Before image. A copy of a record before a change has been made. It is used for backward recovery. Benchmarking. The establishment of goals based on best industry practices. Binary digit. The smallest unit of information capable of being represented in a computer or communication system. Binary relationship. A relationship between exactly two entities. Binary search. A search method in which a list of items is successively halved until the sought item is located. Bit. Short for binary digit. Bits per second. The number of bits of information that pass a given point in one second. A measure of the carrying capacity of a channel. BLOB (binary large object). BLOBs contain large binary data files. Boolean.. A data type that can be true or false. Bottom-up design. In software development, a technique that starts with the parts or most basic functional components and proceeds to build a whole or complete program. Boyce-Codd normal form. A relation in third normal form in which every determinant is a candidate key. B-tree.. A file in which the records are structured into an inverted tree based on a series of midpoints. For example, the root of the tree is the midpoint of a file, and more midpoints occur in each succeeding level. Built-in function. An SQL function such as AVG, COUNT, MAX, MIN, or SUM. Byte. A sequence of eight consecutive bits used in coding systems to represent one character of data or information.
C
C. A high-level programming language that is very popular because of its transportability between computer systems. Candidate key. An attribute or group of attributes that is a potential primary key for a table. Cardinality. The number of rows in a relational table. Cartesian product. A relational operation on two tables, A and B, that produces all possible combinations of the concatenation of a row from A and a row from B. Catalog. A database that contains details of databases. CD-ROM. An acronym for compact disk-read-only memory. An optical disk on which data are encoded for retrieval by a laser. Change agent. A person leading or guiding an organizational change. Change information. Information that helps managers determine which actions might successfully close the gap between actual and desired performance. Channel. A pathway for the transmission of data or information to and from a computer or communication system. Child. A row on the many side of a 1:m relationship. Class. In object-oriented programming, a generalized category that describes a group of objects that can exist within it. The class serves as the template from which specific objects are created. Client. An end user or computer program that requests resources across a network. Client/server computing. A combination of clients and servers that provides the framework for distributing files and databases across a network. In a database, client/server describes the situation where a client runs a database application (front end) that accesses information from a DBMS on a server (back end). CLOB (character large object). CLOBs contain large character data files. Clustering. Storing in the same area, or adjacent physical areas, records that are frequently accessed together. COBOL. An acronym for COmmon Business Oriented Language. A high-level programming language that is used primarily for business-oriented applications. CODASYL/DBTG. The task group that developed the network data model. Code. (1) A set of symbols, such as the dots and dashes of the Morse code, that represents another set of symbols, such as the letters of the alphabet. (2) The set of rules that defines the way in which bits can be arranged to represent numbers and letters. Example: ASCII. (3) To write a computer program in a specific programming language. Column. A vertical group of facts in a table. All values in a column have the same meaning. Command. An instruction that tells a computer to perform an operation. COMMIT. An SQL command to make a set of database changes permanent. Communicability objective. The notion that a database model should facilitate effective and efficient communication between users and IS personnel. Communication. (1) A process by which information is exchanged between individuals through the use of a commonly agreed-on set of symbols. (2) From an engineering standpoint, the movement of electronic traffic from one point to another. Communication server. A device that connects local-area networks (LANs) to wide-area (WANs) or telecommunication networks. Communication software. Programs that enable a computer to connect to other computers and exchange information. Communication system. A system that consists of senders (transmitters), physical channels, and receivers. Compatibility. (1) The ability to connect different computer systems, devices, or software so they can work together. (2) The capability of different computer systems to process the same applications. Compiler. A computer program (software) that reads a high-level program to (1) check it for spelling and grammatical errors and (2) translate it into lower-level language instructions. Complete database language. A language that can be used for defining a database, creating views, specifying queries, and modifying records. Complete programming language.. A general purpose programming language that can be used to write an entire application (e.g., COBOL). Complex service.. A nonstandard service for an object. Composite key. A key with more than one attribute or column. Composition. A structure in which one object is composed of others. Also known as a whole/part structure. Compression. Techniques for compacting data so that they require less storage space. Computer address. (1) The address of a location within a computer’s memory. (2) The Internet identification code of a computer (e.g., arches.uga.edu). Computer-aided design (CAD). The use of a computer system to aid the process of design. Computer-aided software engineering (CASE). A set of tools to automate the tasks involved in designing and developing large-scale or complex software projects. Included are data dictionaries, diagram generators, prototyping tools, and consistency-checking tools. Conceptual schema. An abstract view of a database. Concurrent program execution. The execution of two or more programs at the same time. They actually take turns using the computer so rapidly that they give the illusion of operating concurrently. Concurrent update control. An error arising when one transaction's changes are overwritten by another transaction's changes. Also known as the lost update problem. Consistent database. A database in which all data integrity constraints are satisfied. Control break reporting. A method of reporting a sorted file with new headers or footers each time the sort key changes. Correlated subquery. A subquery that cannot be evaluated once and for all before the outer query is evaluated. The inner query depends on a variable that changes in the outer query. COUNT. An SQL built-in function for determining the number of values in a column. CREATE INDEX. An SQL command to create an index. CREATE TABLE. An SQL command to create a table. CREATE VIEW. An SQL command to create a view. Culture. The set of shared beliefs, values, attitudes, and norms that influences the behavior and expectations of each person in a group. Cursor. A pointer indicating the row to be processed when using embedded SQL. Cycle time. The time taken to complete an activity. Cylinder. The imaginary surface composed of all the tracks that lie directly above and below one another on a multiple-platter disk pack.
D
Data. A general term meaning the facts, numbers, letters, and symbols processed by a computer or communication system to produce information. Data access control. Procedures for controlling which individuals, departments, groups of people, transactions, terminals, or application programs can access data. Data administration. The administration of an organization’s data resources. Data administrator. A person responsible for data administration. Database. (1) A collection of different types of data organized according to a structure that minimizes redundancies and facilitates the manipulation of the data. (2) A collection of one or more files treated as a whole unit. Database administration. (See data administration.) Database administrator. (see data administrator.) Database architecture. A general model for the storage of organizational data. Database development life cycle (DDLC). The stages of developing and maintaining a database. Database integrity. Techniques for protecting a database from invalid alteration, destruction, or access and ensuring data are accurate and reliable. Database machine. A special purpose computer designed for processing databases. Database management system (DBMS). Software that organizes, manipulates, and retrieves data stored in a database. Database server. Software that services requests to a database across a network. Database system . An information system that integrates a collection of data and makes them available to a wide variety of people in an organization. Database transaction. A group of database modifications treated as a single unit. Data communications. The transfer of data or information between computer-related devices. Data communications manager. Software that manages communication between computers and devices. Data definition language (DDL). A language for describing the structure of a database. Data dictionary/directory system (DD/DS). (1) In systems design, a listing of all the data elements and data structures within a system. (2) In a database system, a file that contains descriptions of relationships among a collection of data. Data Encryption Standard (DES). An encryption system developed by IBM and approved in 1976 by the U.S. National Bureau of Standards for governmental use. Dataflow diagram. A graphical method for illustrating business processes. Data independence. The ability of a database to exist independently of specific applications. Data integrity. Techniques for protecting data from invalid alteration, destruction, or access and ensuring data are accurate and reliable. Data item. A field or attribute in DL/I and the network model. Data management. The management of an organization’s data resources. Data manipulation language (DML). A language for describing the processing of a database. Data mart.. A subject-specific data warehouse; often departmental or line-of-business. Data mining.. Knowledge discovery process of extracting previously unknown, actionable information from very large databases. Data model. A graphical description of the entities, attributes, identifiers, and relationships in a database. Data model quality. An assessment of the degree to which a data model is well-formed and its fidelity of image. Data processing. A general term that stands for all the logical, arithmetic, and input/output operations that can be performed on data by a computer. Data quality.. The accuracy, completeness, and currency of data. Data security. Techniques for protecting a database against access or modification without authorization. Data steward. A person responsible for managing all corporate data for some critical business-related unit or activity. Data structure. An organizational scheme used to structure or organize data so that they can be stored, retrieved, and manipulated by a program. Examples include records, lists, and arrays. Data type. A data format (e.g., integer) that can be defined for a column. Data visualization.. Graphical rendering of information from a database. Data warehouse. . A subject-oriented database designed specifically for decision support. DBMS/server. A server that runs a DBMS and processes actions on the database at the request of client programs. Deadlock prevention. A technique for resolving or avoiding a deadly embrace. Deadly embrace. A condition that can occur when two transactions are competing for the same resources. Both transactions are waiting to access data the other transaction has locked. Also known as deadlock. Decision making . The process of identifying and selecting a course of action to solve a specific problem. Decision quality. An assessment of the decision making process. Decision support system (DSS). An interactive, user-friendly system for supporting decision makers. Decode. To modify information from a computer-readable form into a form that people can read or use. Decryption. The decoding of an encrypted electronic transmission. (See also encryption.) Degree. The number of columns in a relational table. DELETE. The SQL command for deleting one or more rows. Dependent entity. An entity that relies on another for its existence and identification. A dependent entity is indicated by a bar on its end of a relationship arc. Also known as a weak entity. Determinant. One or more attributes that functionally determine another attribute or attributes. In the case where A _ B, A is the determinant. Difference. A relational algebra operation on two union-compatible relations A and B, where the new relation contains all rows in A that are not in B. Digitizing. The process of translating analog data into digital data. Direct-access file. A type of file organization scheme designed for processing records in an order other than sequential. Also called a random-access file. Disk. A circular platter on which a magnetic or reflective coating is applied. Used for long-term storage of data. Disk array. The combination and synchronization of multiple disk drives into one self-contained unit. A disk array features faster data access and higher data throughput than an equivalent-sized single disk drive. Disk cartridge. Removable disks that are sealed in a container similar to a videotape cartridge. Disk drive. A device that houses the motor to spin the disk and the read/write head for accessing and storing information on the disk. Disk manager. A part of the operating system responsible for physical I/O. Disk pack. A removable stack of hard disks joined together by a common spindle. DISTINCT. The keyword used in a SELECT statement to indicate that duplicate rows should be eliminated. Distributed computing. A type of processing that uses a number of small computers distributed throughout an organization. Distributed database. A capability in which different parts of a database reside on physically separate computers. The goal is to access information without regard to where the data might be stored. Distributed query processing. Query processing when a database is distributed. Distributed transaction processing. Transaction processing when a database is distributed. Divide. A relational algebra operation that in its simplest form creates a new relation (the quotient) from binary (the dividend) and unary (the divisor) relations. The result of dividing A (the dividend) by B (the divisor) is C (the quotient) is such that for every value of x in C, the pair (x,y) appears in A for all values of y in B. DL/I (Data Language I). IBM’s language to define and process a hierarchical database. Document. Any text or collection of characters (letters, numbers, spaces, punctuation marks, and other symbols); usually associated with word processing and desktop-publishing applications. Documentation. (1) The books, manuals, or tutorials that accompany a computer-related product. (2)Written specifications that are a part of the process of developing software. Domain. The set of all possible legal values of an attribute. DROP INDEX. The SQL command to delete an index. DROP TABLE. The SQL command to delete a table. DROP VIEW. The SQL command to delete a view. Dynamic model. A representation that describes what a system actually does for any particular event.
E
EBCDIC. An acronym for Extended Binary-Coded Decimal Interchange Code. An eight-bit code designed by IBM that assigns binary digits to specific symbols. Used primarily by IBM computers. Electronic brainstorming. The use of computer and communications technology to help a group generate ideas. Electronic conference. A meeting that is conducted over an electronic network using terminals or personal computers. Embedded SQL. SQL statements enclosed within the structure of a general purpose programming language. Empowerment. The act of delegating power and authority to subordinates to further organizational goals. Encapsulation. The concept whereby data and processes contained within an object are not visible to and cannot be changed by other objects. Encryption. The coding of an electronic transmission for purposes of security or privacy. End user. A person who uses a product, as opposed to a person who develops or markets the product. Entity. Something in the real world that is represented in a data model and about which data must be stored. An entity is the basic building block of a data model. Entity integrity. Every instance of an entity defined in a relational database is uniquely identified. Entity-relationship (E-R) model. A data model constructed following the principles of the E-R approach to data modeling. Equijoin. A join containing both matching columns. Erasable optical disk. An optical disk that uses lasers to read and write information to and from the disk, but also uses a magnetic material on the surface of the disk and a magnetic write head to achieve erasability. Exabyte (Ebyte). A unit of measure equivalent to 1015 bytes. Exclusive lock. A lock on a data resource that prevents any other transaction from reading or updating the resource. Exhaustive class. A subclass or a set of subclasses in an inheritance structure that by covering all the relevant objects results in the superclass containing no objects. EXISTS. The SQL implementation of the existential quantifier. EXISTS is used in a WHERE clause to test whether a table contains at least one row satisfying a specified condition. It returns the value true if and only if some row satisfies the condition; otherwise, it returns false. Expert system. A computer program that solves specialized problems at the level of a human expert. External database. A database maintained by a party external to an organization. External memory. Additional memory that is not contained within a system. External schema. A user’s view of a database.
F
Fault-tolerant computer. A computer that uses redundant hardware or software components to prevent failure from disrupting the operation of the system. The system can continue processing while the faulty component is replaced or repaired. Field. The smallest unit of named data that has meaning in a record. A field usually describes an attribute of the record, such as a name or address. Fifth normal form. A relation is in fifth normal form (5NF) if and only if every join dependency of the relation is a consequence of the candidate keys of the relation. File. A collection of organized data stored as one complete unit for processing. File manager. A single file, its indexes, and a program to handle basic tasks, such as entering, modifying, retrieving, and printing data from the file. File server. Software that services requests to a file across a network. First normal form. A relation is in first normal form (1NF) if and only if all columns contain atomic values only. Flat file. A single file consisting of rows (records) and columns (fields) of data that resemble a two-dimensional spreadsheet. Floppy disk. A flexible plastic disk coated with a magnetic recording material. Foreign key. An attribute that is a primary key in the same table or another table. It is the method of recording relations in a relational database. Fourth-generation language. A term that encompasses (1) presentation languages, such as query languages and report generat-ors; (2) specialty languages, such as spreadsheets and database languages; (3) application generators that define, input, modify or update, and report data to build applications; and (4) very high-level languages that are used to generate application code. Often abbreviated as 4GL. Fourth normal form. A relation is in fourth normal form (4NF) if it is in BCNF and all multivalued dependencies on the relation are functional dependencies. Full-text retrieval software. Software that allows text to be indexed, edited, annotated, linked, and searched for in an electronic document. Fully relational database. A relational database system that supports structures (domains and relations), integrity rules (primary and foreign keys), and a manipulation language (relational algebra). Functional dependency. A relationship between attributes in which one attribute or group of attributes determines the value of another. It is shown as A _ B and read as “A determines B” or “B is functionally dependent on A.”
G
Gap information. Information that reveals a gap between desired and actual performance (e.g., an exception report). Generalization/specialization. A structure in which one object generally describes more specialized objects (e.g., transportation is a generalization of car). Geographical information system (GIS). A system that digitizes maps and images of distributions of statistical data and displays them as graphics. Gigabyte (Gbyte). A unit of measure that is the equivalent of 109 bytes. Global change. Change occurring in many different countries simultaneously. Goal-setting information. Information that helps managers to set realistic targets for expected performance. GRANT. An SQL command for granting privileges to a user or users. Granularity. The level of database resources that can be locked. Locking at the database level is large granularity. Locking a column or row is low granularity. Graphical user interface (GUI). An interface that uses pictures and graphic symbols to represent commands, choices, or actions. Graphics. The term encompassing several elements, including color, motion, and resolution, that together result in the ability of a computer to show line drawings, pictures, or animation on a display screen or printer. Differs from an image in that it can contain embedded information. GROUP BY. The SQL phrase for rearranging a table into groups so that all rows in a group have the same value for a specified column. Groupware. Application software that supports collaborative work and integrates applications such as electronic mail, conferencing, calendar and scheduling software; workflow software, which automates the routing of business processes and forms over a network; document management software to handle the creation and revision of shared documents on a network; and group support software to facilitate electronic meetings.
H
Hard disk. A disk made of a rigid base, such as aluminum, and coated with a magnetic-oxide layer. Hash function. The function for computing a hash address from a hash field. Hashing. A mathematical technique for assigning a unique number to each record in a file. HAVING. The SQL keyword specifying the condition the groups returned by a GROUP BY clause must satisfy. HAVING is to groups what WHERE is to rows. Hierarchical model. A method for storing data in a database that structures data into an inverted tree in which records contain (1) a single root or master key field that identifies the type, location, or ordering of the records, and (2) a variable number of subordinate fields that defines the rest of the data within a record. High fidelity image. A data model that faithfully describes the world it is meant to represent. Homonym. One of a group of words pronounced or spelled the same way but having different meanings. Host/terminal. A data processing architecture based on using terminals to access a host computer that stores and processes data. Hybrid architecture. A relatively integrated mix of data processing and storage architectures that has developed over time. Hybrid object relational model. A data model that combines features of the object and relational models. Hypermedia. An extension of hypertext that includes graphics, video, sound, and music. Hypertext. Electronic files in which an author can link information and create nonlinear paths through related material.
I
Identifier. An attribute or collection of attributes that uniquely distinguishes an entity. Images. Data in the form of pictures. Differs from a graphic in that they do not contain embedded information. Image scanner. A device that converts optically focused images, such as photographs or drawings, into digital images that can then be processed like any other digital data. A photoreceptor device is required to convert reflected light into digital images. Imaging system. Information technology that converts paper documents to electronic images. Impedance problem. The mismatch between set-at-a-time processing of a relational database and record-at-a-time processing of programming languages. IMS. Information Management System. IBM’s transaction processing system that includes a data communications monitor (IMS/DC) and an implementation of DL/I (IMS/DB). IN. An SQL keyword preceding a set of values to be searched (e.g., FNAME IN (‘Tom’, ‘Dick’, ‘Harry’)). Independent entity. An entity that is central to a data model and often prominent in the client’s mind. It often has a single, arbitrary identifier. Index. A list containing an entry for each record in a file organized in a certain way. Index sequential. A file organization method that provides both sequential and direct-access capability. Index set. A tree structure providing fast direct access to records in a B-tree. Information. Data transformed into a form and content relevant for a particular situation. Information delivery system. A system that provides information to those who need it. Information engineering. A general approach using CASE tools to develop an enterprise-wide plan for systems development and maintenance. Information hardness. A subjective measure of the accuracy and reliability of some information. Information integration. The process of assembling data in many forms and from many sources to satisfy a user’s needs. Information organization. An organization that relies on information to create profitable products and services. Information processing. The work that information systems perform, consisting of responding to input, processing that input according to instructions, and providing output. Information requirements. A specification of the information a user or group of users needs to solve problems. Information revolution. (1) A term used to indicate the point at which modern society shifted from being an industrial society to being an information society. No agreed-on date. (2) The reshaping of economic, social, political, and technical structures resulting from the teaming of people and computers. Information richness. The concept that information can be rich or lean depending on the information delivery medium. Information satisficing. The practice of decision-makers collecting enough information to make a satisfactory decision. Information service. A business specializing in the collection and distribution of information. Information society. A society structured around the principles of information as a commodity and as a strategic resource. Information superhighway. The concept that every home and business will be connected electronically over a vast network of links to a wide variety of sources of information and entertainment. Information system. A system that takes input, processes it, and produces information as output. Information Systems. A department within an organization that helps people put information to work. Information technology. A collective term for computer-and-communication hardware and system-and-application software. Inheritance. In object-oriented programming, the passing along of certain behavior and structure from a class to its descendants. Inheritance allows new objects to be created from old ones. INSERT. The SQL command for adding one or more rows to a table. Instance. A particular occurrence of an entity. Integrity constraints. Rules and procedures for maintaining data integrity. Interfile clustering. Clustering is applied to records in several files. Internal memory. Memory contained within a system. Internal schema. A low-level description of a database. It specifies data types for fields and may indicate other physical details. Internet. A worldwide network of computers and computer networks at private organizations, government institutions, and universities, over which people share files, send electronic messages, and have access to vast quantities of information. Intersect. A relational algebra operation performed on two-union compatible tables, A and B, that results in a new table containing the rows that are in both A and B. Intrafile clustering. Clustering is applied to records within a single file. Inverted list. An alternative term for an index. ISO. International Standards Organization. Isolation. A preventive strategy that involves administrative procedures to insulate a physical database from destruction.
J
Join. A relational algebra operation on two tables, A and B, that produces a new table containing the concatenation of a row from A and a row from B where the rows in A and B satisfy a specified condition (e.g., column (a) of A = column (b) of B). Journal. A file containing a record of database changes or transactions.
K
Key. A field in a file used to identify records for purposes of retrieval or sorting. Kilobyte (kbyte). A unit of measure equal to 210 or 1024 bytes. Knowledge. The capacity to request, structure, and use information. Knowledge base. The collection of facts, data, beliefs, assumptions, and heuristic methods about a problem area. Knowledge work. A term used for occupations in which the primary activities involve receiving, processing, and transmitting information. Often called information work.
L
Layer. A level of detail of an OO model. Legacy system. A system developed using prior technology that must be maintained because it still provides useful information or processes important business transactions. Legal strategies. Externally imposed laws, rules, and regulations for maintaining data integrity. LIKE. The SQL keyword preceding a description of characters to be searched for within a particular column (e.g., FNAME LIKE ‘%Fred%’). Linked list. A data storage structure that maintains relationships between records using pointers. Local-area network (LAN). A communication channel along with interface circuitry that connects devices, such as computers or peripherals, within a limited geographical distance. Locking. Allocating a particular database resource to a transaction or user. Log. A file containing a record of database changes or transactions. Logical record. A record that is defined according to its content or function. Loop. A series of program instructions that is performed repeatedly until a specified condition is satisfied.
M
Magnetic disk. A direct access storage device that uses magnetization and demagnetization to store data on a magnetic surface. Magnetic tape. A sequential access storage device that uses magnetization and demagnetization to store data on a magnetic surface. Magneto-optical disk. A read-write optical disk. Mainframe. A class of computer providing large storage capacity, high-speed processing, and complex data-handling capabilities. Management information system (MIS). A system that gathers, condenses, and filters data until they become information, then makes them available on time and in a useful form for use in decision making at various levels of management within an organization. Managerial work. A manager’s typical behavior and activities when working. Many-to-many recursive relationship. A relationship within a single entity in which one instance in the entity can be related to many instances in the same entity, and any instance receiving multiple relationships can itself be related to many instances in the same entity. Many-to-many relationship. A relationship between two entities in which one instance in the first entity can be related to many instances in the second entity, and one instance in the second entity can be related to many instances in the first entity. Mass storage. A high-capacity storage device that is typically slower than magnetic disk but less costly per megabyte. Master file. A type of file that can be thought of as a relatively permanent collection of records. Matrix organization. An organizational structure in which an employee reports to both a functional or divisional manager and to a project or group manager. MAX. An SQL built-in function for determining the largest value in a column. Megabyte (Mbyte). A unit of measure that is the equivalent of 106 bytes. Member. A record type that is at the many side of a 1:m relationship in the CODASYL/DBTG model. Memory. The component of a computer system that stores programs and data while waiting to be processed by the CPU. Also called primary storage. Message passing. The method by which objects can communicate. Method. A set of instructions attached to an object. Also known as a service. Micro. (1) In precise measurement, a prefix meaning one millionth. (2) In inexact measurement, a prefix meaning small. (3) Short for microcomputer. Microcomputer. A computer system based on a single-chip microprocessor as the central processing unit. Microsecond. A measure of time equivalent to one-millionth (1/1,000,000) of a second. Middleware. A layer of software between the network and applications that provides services such as data transportation, service roaming, directory lookup, data access, transaction monitoring, and security. Middleware allows applications to communicate more easily and effectively. A JDBC driver is data-access middleware. Millisecond. A measure of time equivalent to one-thousandth (1/1,000) of a second. MIN. An SQL built-in function for determining the smallest value in a column. Minicomputer. A type of medium-sized computer introduced in the 1960s that provides lower-cost processing and storage capacities than the larger mainframe computers. MIPS. An acronym for million instructions per second. Most often used as a unit of measure for comparing the processing speed of different computers. Mirroring. The technique of writing identical copies of a record to each drive of a RAID unit. Multimedia. The combination of text with dynamic data types such as sound, animation, and video. Multiprocessing. A computer system that uses two or more processors that share memory and input and output devices. Multiprogramming. A computer system in which two or more programs are executed concurrently by one computer. In effect, the programs take turns running, usually giving the user the illusion of being the only user of the system. Multitasking. A technique for concurrently executing tasks, or basic units of work performed by a program, on the same computer system. It is similar to multiprogramming, except the processor may be working on several portions of a program instead of several programs. Multiuser. Systems that allow several users to share a computer’s processor, memory, and mass storage simultaneously. Often characterized by systems with several terminals connected to a single central processor. Multiuser database. A database that can be concurrently accessed by more than one person or transaction.
N
Nanosecond. A measure of time equivalent to one-billionth (1/1,000,000,000) of a second. Natural join. A join from which one of the matching columns has been deleted. Natural-language interface. An interface that allows the user to input simple English or other natural-language phrases in lieu of complex computer commands. Network. An interconnected system of computers. Network data model. A data model supporting network relationships. Network model. A technique used in database systems to store data by combining records with a linked list of pointers. Node. The term for a device, such as a terminal, computer, or disk drive, connected to a communication network. Normal form. One or more rules for governing the structure of tables. Normalization. The process of converting a table in low normal form to a higher normal form. NOT. The SQL keyword to select the opposite of a condition (e.g., NOT EXISTS). NOT EXISTS. The negative of EXISTS. It is used in a WHERE clause to test whether all rows in a table do not satisfy a specified condition. It returns the value true if there are no rows satisfying the condition; otherwise, it returns false. Null. A value that may be unknown, not required, not applicable, undefined, or missing. It is not a blank or zero.
O
Object. A module that contains both data and instructions and can perform specific tasks. In software engineering, an object is an instance of a class or a logical grouping of objects. Object class. A set of objects with a common structure. Object code. Output from a compiler or an assembler that is linked with other code to produce executable machine-language code. Object data language (ODL).. A language for defining objects. Object data model (ODM). A defined set of built-in types that is used to create and represent composite structures that mirror real-world objects. Object identifier. An attribute used to uniquely identify an object. Object Management Group (OMG). An industry group with the goal of creating and promulgating standards for OO technology and object interaction. Object model. In database systems, data and instructions are combined into objects--modules that perform specific tasks when they are sent an appropriate message. Object-orientation (OO). An approach to systems development, design, and programming based on object concepts. Object-oriented Database Management System (ODBMS). Software that organizes, manipulates, and retrieves data stored in an object-oriented database. Object-oriented programming. A technique in which the programmer breaks the problem into modules called objects, which contain both data and instructions and can perform specific tasks. The programmer then organizes the program around the collection of objects. An example is Smalltalk. One-to-many (1:m) recursive relationship. A relationship within a single entity in which one instance in the entity can be related to many instances in the same entity, and any instance receiving multiple relationships is itself related to only one instance. One-to-many (1:m) relationship. A relationship between two entities in which one instance in the first entity can be related to many instances in the second entity, and an instance in the second entity can be related to at most one instance in the first entity. One-to-one (1:1) recursive relationship. A relationship within a single entity in which one instance in the entity can be related to at most one instance in the same entity, and an instance receiving a relationship can itself be related to at most one instance in the same entity. One-to-one (1:1) relationship. A relationship between two entities in which one instance in the first entity can be related to at most one instance in the second entity, and an instance in the second entity is related to at most one instance in the first entity. On-line analytical processing (OLAP). Analyzing business operations with the intention of making timely and accurate analysis-based decisions. OO model. A graphical representation of objects in an application. OO programming language (OOPL). A language that supports the OO concepts. Optical disk. Disks that record and retrieve data using laser beams of light instead of magnetic methods. There are three types of optical disks: read only, also called CD-ROM; write once, which can be recorded on once by the end user; and erasable, which combines optical and magnetic techniques to record on the surface of the disk. ORDER BY. The SQL clause for identifying columns on which to sort rows. Organizational change. The adoption of a new idea or behavior by an organization. Organizational memory. An organization’s record of the details necessary for transacting business and making decisions. Owner. A record that is at the one end of a 1:m relationship in CODASYL/DBTG database.
P
Page. A unit of disk storage. Parent. A row on the one side of a 1:m relationship. Parity. A bit, used for error checking, that is part of a binary code that indicates the number of 1’s in the code. Password. A unique, usually secret code used to identify users, which allows them to access a system. The system can be accessed by multiple users. Performance monitoring. Collecting statistics on the performance of a system (e.g., number of transactions per minute). Peripheral. A device that operates in conjunction with--but is not a part of--a computer, such as a printer, disk drive, or graphics tablet. Persistent object. An object that exists between executions of a program. Personal computer. A microcomputer usually targeted to the information processing needs of an individual, often called a microcomputer. Petabyte (Pbyte). A unit of measure equivalent to 1015 bytes. Physical file. The way in which the actual data in a database system are stored and accessed on a medium such as a disk. Physical record. A record that is composed of one or more logical records. Pointer. An address that specifies a storage location where data can be found. Polymorphism. The capability to send a common message to objects of different types. Each object will respond with its own particular behavior. Primary key. The candidate key selected as the unique identifier of a row in a table. Product. A relational operation on two tables, A and B, that produces all possible combinations of the concatenation of a row from A and a row from B. Project. A relational algebra operation that creates a new relation from some of the columns of an existing relation. Project level database administration. Management and support of the development and use of a specific database system. Protocol. A formal set of rules for specifying the format and relationships when exchanging information between communicating devices. Prototyping. The process of building working models of a system’s inputs, outputs, and files. Public key encryption. An encryption system comprising public and private keys. The public key can be freely distributed because it is quite separate from the private key.
Q
Qualified name. The name of a column when it is prefixed by the name of the table in which it is found (e.g., STOCK.STKPRICE). Query. A question or request for information. Query by example (QBE). A fill-in-the-blanks approach to questioning a database. The user searches for information by filling out a query form on the display screen. Query language. The capability to question a database or file of information without any knowledge of how or where the information is stored.
R
RAID. An acronym for a redundant array of inexpensive or independent drives. It uses a combination of mirroring and striping to give greater data protection. RAM. An acronym for random-access memory. Its name comes from the method used to access information from the memory: random access. This means that it takes the same amount of time to access any one piece of information as it does another. Random-access device. A device that can read and write information at any location on the device in the same amount of time, regardless of its physical location. Random-access method. A method of accessing a file that allows a program to read or write any record in the file in the same amount of time without regard to its physical location. Rapid application development. An approach to application development that stresses completion of a system in a short period. Read-only optical disks. Optical disks that cannot be written on and so have the functional equivalency of read-only memory (ROM). Record. A collection of related data treated as a unit (e.g., the payroll data about one person). Recovery. The process of restoring a database to a consistent state. Recursive relationship. A relationship within a single entity (e.g., a monarch is preceded by one other monarch). Referential integrity constraint. The requirement that a foreign key cannot be defined unless its corresponding primary key exists. Relation. A two-dimensional table in the formal terminology of relational databases. Relational algebra. A set of high-level operators that operates on relations. Relational database. A database consisting of relations or tables. Relational Database Management System (RDBMS). Software that organizes, manipulates, and retrieves data stored in a relational database. Relationally complete. A relational database management system that supports SQL but not domains or integrity rules. Relational model. A technique used in database systems in which one or more flat files or tables create relationships among the tables on the basis of a common field in each of the tables. Relationship. An association between entities or objects. Relationship descriptor. A description of a relationship. Remote job entry. The electronic submission of a program to be executed on a remote computer. Replication. Maintaining copies of a database at several sites. Request for proposal (RFP). A document sent to vendors seeking their response to a list of mandatory and optional capabilities and features. Requirements planning. A broad term that includes planning for outputs, inputs, file/storage, and processing require-ments. It also includes specifying any constraints and the costs and benefits associated with the system. Resource Description Framework (RDF). A general framework for how to describe any Internet resource such as a Web site and its content. Restrict. A relational algebra operation that creates a new relation from some of the rows of an existing relation. This operation is sometimes called select but should not be confused with the SQL SELECT statement. REVOKE. An SQL command for removing privileges from a user or users. Rollback. The process of recovering a database by applying before images to return the database to a consistent earlier state. ROLLBACK. An SQL command to reverse a set of temporary database changes. Roll forward. The process of recovering a database by applying after images to bring the database to a consistent state. ROM. An acronym for read-only memory. A permanent memory whose contents can neither be erased nor written over--thus, the name, read-only memory. Root. The top record or node in a tree. Row. All columns in a table pertaining to the same instance of an entity (e.g., all the facts about a share).
S
Scalar function. A function operating on a single value (e.g., DAYS). Scanner. A device that examines a pattern and converts it into a digital representation suitable for computer processing. Patterns then can be manipulated into a form suitable for the application. Scenario. A typical event or sequence of events in the problem domain and the related behavior of the information system. Search time. The time required to rotate the needed record under the read/write head of a magnetic disk. Secondary index. In DL/I, an index on a data item other than the primary key. Secondary storage. The component of a computer system in which programs and data are stored while not in use. Second normal form. A relation is in second normal form (2NF) if and only if it is in 1NF and all non-key columns are dependent on the key. Sector. The smallest block of physical data that can be written to or read from a disk device. Security. Precautions taken to ensure that data are protected from unauthorized use or modification. Seek time. The time required to position the read/write head over the proper track on a magnetic disk. Segment. In DL/I, a collection of fields that constitutes a node in a database record. SELECT. The SQL command for retrieving rows from a database. Sequence set. A single-index to the data in a file. Sequential file. A file organization method that involves storing records in a predetermined sequence based on one or more key fields. Server. A computer running software that fulfills requests from clients across a network. Service. A set of instructions attached to an object. Also known as a method. Servlet. A Java program that runs inside a Java-based Web server or Java applications server. Set. A structure for representing a 1:m relationship in the CODASYL/DBTG model. Set processing. The capability of a language to process multiple records at a time. Shareable data. Data that can be readily accessed, not necessarily simultaneously, by more than one person. Simple service. A standard service that most objects need to be able to perform (e.g., create). Social memory. A society’s record of the details necessary for maintaining itself. Social network. A relationship between a group of people. Software. Programs that control the functions of a computer system. Sparse index. An index that does not contain an entry for every record. Also called a non-dense index. Special registe. r. In SQL, a built-in value (e.g., CURRENT DATE). SQL (Structured query language). A query language that manipulates data in a relational database. Standard operating procedures. The rules and procedures for handling routine or common tasks. Static model. A representation that shows what objects are capable of doing and remembering. Storage device. A device (e.g., filing cabinet or hard disk) for storing data. Storage medium. The material used for storing data (e.g., paper, magnetic film). Storage structure. A formalized arrangement for storing data. Strategy. A plan of action designed to cope with change, competition, and uncertainty. Streaming tape. A form of magnetic tape that is specifically designed to store backup copies of disk files. Also called cartridge tape. Striping. The technique of writing different parts of a record and parity data to different drives in a RAID unit. Structured analysis. The examination of a complex problem by dividing it into simple functions. Structured design. The process of designing the components of a computer program and their interrelationship in the best possible way. Structured programming. The application of top-down design methods to programming. Subclass. In a generalization/specialization hierarchy, an object that is a specialization of the generalization. Subject. A cluster of objects. The subject layer reduces the overall complexity of an OO model. Subordinate entity. An entity that stores data about an entity that varies among instances. It is used when an entity consists of mutually exclusive classes that have different descriptions. Subquery. A query nested within another query. Subroutine. A part of a program that can be executed repeatedly by a single statement. SUM. An SQL built-in function for determining the sum of values in a numeric column. Superclass. In a generalization/specialization hierarchy, the collection of objects that makes the generalization. Supercomputers. The fastest computers made. Synonym. A word that means the same as another word. SYSCATALOG. In SQL, a catalog table containing a row for every base table or view in the database. SYSCOLUMNS. In SQL, a catalog table containing a row for every column of every table in the database. SYSINDEXES. In SQL, a catalog table containing a row for every index in the database. System. (1) In general systems theory, a set or arrangement of parts acting together to perform a function. (2) In systems analysis, a network of interrelated procedures performed by people with the aid of tools or machines. System level database administration. Management of issues applicable to the entire database environment and all databases managed within that environment. Systems analysis. The process of understanding a user’s needs and, from those needs, deriving the functional requirements of a system. Systems development life cycle (SDLC). The stages of developing and maintaining a system. System software. Programs or commands used to control the operation of the computer system.
T
Table. In relational database terminology, a table consists of rows and columns. Each row identifies a record, and each column corresponds to a field. Also called a relation. Talk. An Internet service supporting real-time conversations. The Internet version of the telephone. Tape drive. A device that stores data recorded on magnetic tape. Technical strategies. Computer-based procedures designed to maintain data integrity. Telnet. The main Internet protocol for connecting to a remote machine. Temporary name. A name given to a table or view that remains current only for the duration of a query. Terabyte (Tbyte). A unit of measure equivalent to 1012 bytes. Terminal. A device that is used in communication systems to enter or receive data. Text database. A collection of words such as articles in the Wall Street Journal or a series of legal abstracts. Text databases are stored either on-line or on CD-ROM and include the means to search through massive amounts of data to answer specific questions. Third normal form. . A relation is in third normal form (3NF) if and only if it is in second normal form and has no transitive dependencies. Top-down approach. A technique used by systems analysts and software developers that refers to starting with the whole problem and developing more and more detail as the solution develops. Track. A concentric circle on which data are stored on a disk. Track density. The number of tracks per inch on a disk. Transaction. An event about which data are recorded and processed, for example, a request for a seat on an airline flight. Transaction file. A type of file in which records created during the input process are stored until needed for further processing. Transaction processing. The processing of transactions. Transitive dependency. The situation in a relation where if A determines B, and B determines C, then A determines C. Transparent. A term used by computer designers to indicate a function of which the user is unaware. Tree structure. A collection of records or other data structures in which the child has at most one parent. Tuple. A row in a two-dimensional database.
U
Uniform Resource Identifier (URI). A URI identifies a point of content (e.g., a page of text or sound clip). The most common form of URI is a Web page address, which is a particular form or subset of URI called a Uniform Resource Locator (URL). A URI typically describes: the protocol to access the resource, the specific computer storing the resource, and the specific name of the resource (a file name). Union. A relational algebra operation on two union-compatible relations A and B, where the new relation contains all rows that are in both A and B, with duplicate rows deleted. Union compatible. The condition that two tables have the same number of columns and that values in corresponding columns are drawn from the same domain. Unique key. A key that cannot have duplicate values. Update. A term for the modification of records in a master file by replacing older information with more current information. UPDATE. The SQL command for updating one or more rows of a table. Use relationship. A communication relationship between objects. User friendly. A term describing how easy a system or program is to learn and use and how gently it tolerates errors or mistakes on the part of the user. Userid. A person’s user identification code. User interface. That portion of a program that handles the human interaction with the program.
V
Validation. The process of ensuring data quality. Video conference. A conference held by means of one- or two-way interactive television. View. A table constructed dynamically from operations on base tables. Also called a virtual table. Voice data. A record of speech or sound. Voice mail. A technology in which spoken messages are digitized, stored in computers, and later retrieved by the recipient. Volatile file. A file in which a high percentage of records accessed are changed or records are added or deleted. VSAM (Virtual Storage Access Method). IBM’s implementation of the B-tree concept.
W
Weak entity. An entity that relies on another for its existence and identification. A dependent entity is indicated by a bar on its end of a relationship arc. Also known as a dependent entity. Weakly typed language. A language in which the compiler or interpreter is not required to check the types of operands to ensure nonsensical operations are not performed. Web Services. XML-based applications, hosted on the Internet, which provide information and services to customers and users around the world. Well-formed data model. A data model that clearly communicates information to the client. It obeys all the construction rules. WHERE. The SQL keyword specifying the condition that the rows returned by a SELECT statement must satisfy. Whole/part structure. An object structure in which one object is composed of others. Also known as a composition. WIMP. Windows, icon, mouse, pointer. Workflow. The manual or electronic flow of work between people.
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