Database Concepts CGS2425 Glossary of Terms

A | B | C | D | E | F | G | H | I | J | K/L | M | N | O | P | Q | R | S | T | U | V | W | X |

Note: The chapter or appendix in which a term is defined is listed in parentheses after the definition.

A

Action An operation, such as create, delete, update, or read, which may be performed on data objects. (4)

Action assertion A statement of a constraint or control on the actions of the organization. (4)

Alias An alternative name used for an attribute. (5)

Anchor object A business rule (a fact) on which actions are limited. (4)

Anomaly An error or inconsistency that may result when a user attempts to update a table that contains redundant data. The three types of anomalies are insertion, deletion, and modification. (5)

Application partitioning The process of assigning portions of application code to client or server partitions after it is written, in order to achieve better performance and interoperability (ability of a component to function on different platforms). (9)

Application program interface (API) Sets of routines that an application program uses to direct the performance of procedures by the computer's operating system. (9)

Associative entity An entity type that associates the instances of one or more entity types and contains attributes that are peculiar to the relationship between those entity instances. (3)

Attribute A property or characteristic of an entity type that is of interest to the organization. (3)

Attribute inheritance A property by which subtype entities inherit values of all attributes of the supertype. (4)

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B

Base table A table in the relational data model containing the inserted raw data. Base tables correspond to the relations that are identified in the database's conceptual schema. (7)

Binary relationship A relationship between instances of two entity types. (3)

Bitmap index A table of bits in which each row represents the distinct values of a key and each column is a bit, which when on indicates that the record for that bit column position has the associated field value. (6)

Blocking factor The number of physical records per page. (6)

Boyce-Codd normal form (BCNF) A relation in which every determinant is a candidate key. (B)

Business function A related group of business processes that support some aspect of the mission of an enterprise. (2)

Business rule A statement that defines or constrains some aspect of the business. It is intended to assert business structure or to control or influence the behavior of the business. (3)

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C

Candidate key An attribute, or combination of attributes, that uniquely identifies a row in a relation. (5).

Cardinality constraint Specifies the number of instances of one entity that can (or must) be associated with each instance of another entity. (3)

Catalog A set of schemas that, when put together, constitute a description of a database. (7)

Client/server systems A networked computing model that distributes processes between clients and servers, which supply the requested services. In a database system, the database generally resides on a server that processes the DBMS. The clients may process the application systems or request services from another server that holds the application programs. (9)

Completeness constraint A type of constraint that addresses the question whether an instance of a supertype must also be a member of at least one subtype. (4)

Composite attribute An attribute that can be broken down into component parts. (3)

Composite identifier An identifier that consists of a composite attribute. (3)

Composite key A primary key that consists of more than one attribute. (5)

Computer-aided software engineering (CASE) Software tools that provide automated support for some portion of the systems development process. (2)

Conceptual schema A detailed, technology independent specification of the overall structure of a database. (2)

Constraint A rule that cannot be violated by database users. (1)

Correlated subquery In SQL, a subquery in which processing the inner query depends on data from the outer query. (8)

Corresponding object A business rule (a fact) that influences the ability to perform an action on another business rule. (4)

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D

Data Facts, text, graphics, images, sound, and video segments that have meaning in the users' environment. (1)

Data control language (DCL) Commands used to control a database, including administering privileges and the committing (saving) of data. (7)

Data definition language (DDL) Those commands used to define a database, including creating, altering, and dropping tables and establishing constraints. (7)

Data independence The separation of data descriptions from the application programs that use the data. (1)

Data manipulation language (DML) Those commands used to maintain and query a database, including updating, inserting, modifying, and querying data. (7)

Data type A detailed coding scheme recognized by system software, such as a DBMS, for representing organizational data. (6)

Data warehouse An integrated decision support database whose content is derived from the various operational databases. (1)

Database An organized collection of logically related data. (1)

Database application An application program (or set of related programs) that is used to perform a series of database activities (create, read, update, and delete) on behalf of database users. (1)

Database management system (DBMS) A software application that is used to create, maintain, and provide controlled access to user databases. (1)

Database server A computer that is responsible for database storage, access, and processing in a client/server environment. Some people also use this term to describe a two-tier client/server environment. (9)

Degree The number of entity types that participate in a relationship. (3)

Denormalization The process of transforming normalized relations into unnormalized physical record specifications. (6)

Derivation A statement derived from other knowledge in the business. (4)

Derived attribute An attribute whose values can be calculated from related attribute values. (3)

Derived fact A fact that is derived from business rules using an algorithm or inference. (4)

Determinant The attribute on the left-hand side of the arrow in a functional dependency. (5)

Disjoint rule Specifies that if an entity instance of the supertype is a member of one subtype, it cannot simultaneously be a member of any other subtype. (4)

Disjointness constraint A constraint that addresses the question whether an instance of a supertype may simultaneously be a member of two (or more) subtypes. (4)

Dynamic SQL The process of making an application capable of generating specific SQL code on the fly, as the application is processing. (8)

Dynamic view A virtual table that is created dynamically upon request by a user. A dynamic view is not a temporary table. Rather its definition is stored in the system catalog and the contents of the view are materialized as a result of an SQL query that uses the view. Distinguish from a materialized view, which may be stored on a disk and refreshed at intervals or when used, depending on the RDBMS. (7)

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E

Embedded SQL The process of including hard-coded SQL statements in a program written in another language, such as C or Java. (8)

Enhanced entity-relationship (ERR) model The model that has resulted from extending the original E-R model with new modeling constructs. (4)

Enterprise data model A graphical model that shows the high-level entities for the organization and the relationships among those entities. (1)

Enterprise data modeling The first step in database development, in which the scope and general contents of organizational databases are specified. (2)

Enterprise key A primary key whose value is unique across all relations. (5)

Enterprise resource planning (ERP) systems A business management system that integrates all functions of the enterprise, such as manufacturing, sales, finance, marketing, inventory, accounting, and human resources. ERP systems are software applications that provide the data necessary for the enterprise to examine and manage its activities. (1)

Entity A person, place, object, event, or concept in the user environment about which the organization wishes to maintain data. (3)

Entity cluster A set of one or more entity types and associated relationships grouped into a single abstract entity type. (4)

Entity instance (instance) A single occurrence of an entity type. (3)

Entity integrity rule No primary key attribute (or component of a primary key attribute) can be null. (5)

Entity type A collection of entities that share common properties or characteristics. (3)

Entity-relationship (E-R) diagram A graphical representation of an entity-relationship model. (3)

Entity-relationship (E-R) model A logical representation of the data for an organization or for a business. (3)

Equi-join A join in which the joining condition is based on equality between values in the common columns. Common columns appear (redundantly) in the result table. (8)

Event-driven Nonprocedural programming that detects an event when it occurs and generates an appropriate response to that event. (9)

Extent A contiguous section of disk storage space. (6)

Extranet Use of Internet protocols to establish limited access to company data and information by the company's customers and suppliers. (1)

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F

Fact An association between two or more terms. (3)

Fat client A client PC that is responsible for processing presentation logic, extensive application and business rules logic, and many DBMS functions. (9)

Field The smallest unit of named application data recognized by system software. (6)

File organization A technique for physically arranging the records of a file on secondary storage devices. (6)

File server A device that manages file operations and is shared by each of the client PCs attached to a LAN. (9)

First normal form A relation that contains no multivalued attributes. (5)

Foreign key An attribute in a relation of a database that serves as the primary key of another relation in the same database. (5)

Fourth normal form A relation in BCNF that contains no multivalued dependencies. (B)

Function A stored subroutine that returns one value and has only input parameters. (8)

Functional decomposition An iterative process of breaking down the description of a system into finer and finer detail in which one function is described in greater detail by a set of other, supporting functions. (2)

Functional dependency A constraint between two attributes or two sets of attributes. (5)

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G

Generalization The process of defining a more general entity type from a set of more specialized entity types. (4)

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H

Hash index table A file organization that uses hashing to map a key into a location in an index, where there is a pointer to the actual data record matching the hash key. (6)

Hashed file organization A storage system in which the address for each record is determined using a hashing algorithm. (6)

Hashing algorithm A routine that converts a primary key value into a relative record number (or relative file address). (6)

Homonym An attribute that may have more than one meaning. (5)

Horizontal partitioning Distributing the rows of a table into several separate files. (6)

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I

Identifier An attribute (or combination of attributes) that uniquely identifies individual instances of an entity type. (3)

Identifying owner The entity type on which the weak entity type depends. (3)

Identifying relationship The relationship between a weak entity type and its owner. (3)

Incremental Commitment A strategy in systems development projects in which the project is reviewed after each phase and continuation of the project is rejustified in each of these reviews. (2)

Index A table or other data structure used to determine the location of rows in a file that satisfy some condition. (6)

Indexed file organization The storage of records either sequentially or nonsequentially with an index that allows software to locate individual records. (6)

Information Data that have been processed in such a way as to increase the knowledge of the person who uses the data. (1)

Information engineering A formal, top-down methodology that uses a data orientation to create and maintain information systems. (2)

Information systems architecture (ISA) A conceptual blueprint or plan that expresses the desired future structure for the information systems in an organization. (2)

Intranet Use of Internet protocols to establish access to company data and information that is limited to the organization. (1)

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J

Join A relational operation that causes two tables with a common domain to be combined into a single table or view. (8)

Join index An index on columns from two or more tables that come from the same domain of values. (6)

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L

Legacy data Data contained by a system used prior to the installation of a new system. Often legacy data resides on mainframe systems, which may have been replaced by client/server systems or Web-enabled systems. (1)

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M

Massively parallel processing (MPP)/shared nothing architecture Massively parallel processing systems where each CPU has its own dedicated memory. (9)

Materialized view Copies or replicas of data based on SQL queries created in the same manner as dynamic views. However, a materialized view exists as a table and thus care must be taken to keep it synchronized with its associated base tables. (7)

Maximum cardinality The maximum number of instances of one entity that may be associated with each instance of another entity. (3)

Metadata Data that describe the properties or characteristics of other data. (1)

Middleware: Software that allows an application to interoperate with other software without requiring the user to understand and code the low-level operations necessary to achieve interoperability. (9)

Minimum cardinality The minimum number of instances of one entity that may be associated with each instance of another entity. (3)

Multivalued attribute An attribute that may take on more than one value for a given entity instance. (3)

Multivalued dependency The type of dependency that exists when there are at least three attributes (e.g., A, B, and C) in a relation, with a well-defined set of B and C values for each A value, but those B and C values are independent of each other. (B)

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N

Natural join Same as equi-join except one of the duplicate columns is eliminated in the result table. (8)

Normal form A state of a relation that results from applying simple rules regarding functional dependencies (or relationships between attributes) to that relation. (5)

Normalization The process of decomposing relations with anomalies to produce smaller, well-structured relations. (5)

Null A value that may be assigned to an attribute when no other value applies or when the applicable value is unknown. (5)

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O

Open database connectivity (ODBC) standard An application programming interface that provides a common language for application programs to access and process SQL databases independent of the particular RDBMS that is accessed. (9)

Outer join A join in which rows that do not have matching values in common columns are nevertheless included in the result table. (8)

Overlap rule Specifies that an entity instance can simultaneously be a member of two (or more) subtypes. (4)

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P

Page The amount of data read or written by an operating system in one secondary memory (disk) input or output operation. For I/O with a magnetic type, the equivalent term is record block. (6)

Partial functional dependency A functional dependency in which one or more nonkey attributes are functionally dependent on part (but not all) of the primary key. (5)

Partial specialization rule Specifies that an entity instance of the supertype is allowed not to belong to any subtype. (4)

Persistent Stored Modules (SQL/PSM) Extensions defined in SQL-99 that include the capability to create and drop modules of code stored in the database schema across user sessions. (8)

Physical file A named portion of secondary memory (a magnetic tape or hard disk) allocated for the purpose of storing physical records. (6)

Physical record A group of fields stored in adjacent memory locations and retrieved and written together as a unit by a DBMS. (6)

Physical schema Specifications for how data from a conceptual schema are stored in a computer's secondary memory. (2)

Pointer A field of data that can be used to locate a related field or row of data. (6)

Primary key An attribute (or combination of attributes) that uniquely identifies each row in a relation. (5)

Procedure A collection of procedural and SQL statements that are assigned a unique name within the schema and stored in the database. (8)

Project A planned undertaking of related activities to reach an objective that has a beginning and an end. (2)

Prototyping An iterative process of systems development in which requirements are converted to a working system that is continually revised through close work between analysts and users. (2)

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Q

Query-by-Example (QBE) A direct manipulation database language that uses a graphical approach to query construction. (9)

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R

Recursive foreign key A foreign key in a relation that references the primary key values of that same relation. (5)

Redundant Array of Inexpensive Disks (RAID) A set, or array, of physical disk drives that appear to the database user (and programs) as if they form one large logical storage unit. (6)

Referential integrity An integrity constraint specifying that the value (or existence) of an attribute in one relation depends on the value (or existence) of a primary key in the same or another relation. (7)

Referential integrity constraint A rule that states that either each foreign key value must match a primary key value in another relation or the foreign key value must be null. (5)

Relation A named two-dimensional table of data. (5)

Relational DBMS (RDBMS) A database management system that manages data as a collection of tables in which all data relationships are represented by common values in related tables. (7)

Relationship instance An association between (or among) entity instances where each relationship instance includes exactly one entity from each participating entity type. (3)

Relationship type A meaningful association between (or among) entity types. (3)

Repository A centralized knowledge base of all data definitions, data relationships, screen and report formats, and other system components. (1, 2)

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S

Scalar aggregate A single value returned from an SQL query that includes an aggregate function. (7)

Schema That structure which contains descriptions of objects created by a user, such as base tables, views, and constraints, as part of a database. (7)

Second normal form A relation in first normal form in which every nonkey attribute is fully functionally dependent on the primary key. (5)

Secondary key One field or a combination of fields for which more than one record may have the same combination of values. Also called a nonunique key. (6)

Sequential file organization The storage of records in a file in sequence according to a primary key value. (6)

Simple attribute An attribute that cannot be broken down into smaller components. (3)

Specialization The process of defining one or more subtypes of the supertype and forming supertype/subtype relationships. (4)

Stored procedure A module of code, usually written in a proprietary language such as Oracle's PL/SQL or Sybase's Transact-SQL, that implements application logic or a business rule and is stored on the server, where it runs when it is called. (9)

Stripe The set of pages on all disks in a RAID that are the same relative distance from the beginning of the disk drive. (6)

Strong entity type An entity that exists independently of other entity types. (3)

Structural assertion A statement that expresses some aspect of the static structure of the organization. (4)

Subtype A subgrouping of the entities in an entity type that is meaningful to the organization and that shares common attributes or relationships distinct from other subgroupings. (4)

Subtype discriminator An attribute of the supertype whose values determine the target subtype or subtypes. (4)

Supertype A generic entity type that has a relationship with one or more subtypes. (4)

Supertype/subtype hierachy A hierarchical arrangement of supertypes and subtypes, where each subtype has only one supertype. (4)

Symmetric multiprocessing (SMP) A parallel processing architecture where the processors share a common shared memory. (9)

Synonyms Two (or more) attributes having different names but the same meaning, as when they describe the same characteristics of an entity. (5)

Systems development life cycle (SDLC) The traditional methodology used to develop, maintain, and replace information systems. (2)

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T

Tablespace A named set of disk storage space in which physical files for database tables may be stored. (6)

Term A word or phrase that has a specific meaning for the business. (3)

Ternary relationship A simultaneous relationship among instances of three entity types. (3)

Thin client A PC configured for handling user interfaces and some application processing, usually with no or limited local data storage. (9)

Third normal form A relation that is in second normal form and has no transitive dependencies present. (5)

Three-tiered architecture A client/server configuration that includes three layers: a client layer and two server layers. While the nature of the server layers differs, a common configuration contains an application server. (9)

Time stamp A time value that is associated with a data value. (3)

Top-down planning: A generic information systems planning methodology that attempts to gain a broad understanding of the information system needs of the entire organization. (2)

Total specialization rule: Specifies that each entity instance of the supertype must be a member of some subtype in the relationship. (4)

Transitive dependency A functional dependency between two (or more) nonkey attributes. (5)

Trigger A named set of SQL statements that are considered (triggered) when a data modification (INSERT, UPDATE, DELETE) occurs. If a condition stated within the trigger is met, then a prescribed action is taken. (8)

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U

Unary relationship A relationship between the instances of a single entity type. (3)

User view A logical description of some portion of the database that is required by a user to perform some task. (1)

User-defined datatype (UDT) SQL-99 allows uers to define their own datatype by making it a subclass of a standard type or creating a type that behaves as an object. UDTs may also have defined functions and methods. (8)

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V

Vector aggregate Multiple values returned from an SQL query that includes an aggregate function. (7)

Vertical partitioning Distributing the columns of a table into several separate physical records. (6)

Visual Basic for Applications (VBA) The programming language that accompanies Access 2000. (9)

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W

Weak entity type An entity type whose existence depends on some other entity type. (3)

Well-structured relation A relation that contains minimal redundancy and allows users to insert, modify, and delete the rows in a table without errors or inconsistencies. (5)

X

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