IT 214 Chapter 2

relational database management system

A collection of programs that manages a relational database. (more on paper)

logical independence

A condition in which the internal model can be changed without affecting the conceptual model. (The internal model is hardware-independent because it is unaffected by the computer on which the software is installed. Therefore, a change in storage devices or operating systems will not affect the internal model.)

physical independence

A condition that exists when the physical model can be changed without affecting the internal model.

network model

A data model standard created by the CODASYL Data Base Task Group in the late 1960s. It represented data as a collection of record types and relationships as predefined sets with an owner record type and a member record type in a 1:M relationship.

Object-oriented data model (OODM)

A data model whose basic modeling structure is an object.

Entity Relationship Diagram (ERD)

A diagram that depicts an entity relationship model's entities, attributes, and relations.

relational diagram

A graphical representation of a relational database's entities, the attributes within those entities, and the relationships among the entities.

Physical Model

A model in which physical characteristics such as location, path, and format are described for the data. The physical model is both hardware- and software-dependent.

software independence

A property of any model or application that does not depend on the software used to implement it.

Conceptual Schema

A representation of the conceptual model, usually expressed graphically. See also conceptual model.

constraint

A restriction placed on data, usually expressed in the form of rules. For example, "A student's GPA must be between 0.00 and 4.00." Constraints are important because they help to ensure data integrity.

Logical Design

A stage in the design phase that matches the conceptual design to the requirements of the selected DBMS and is therefore software-dependent. Logical design is used to translate the conceptual design into the internal model for a selected database management system, such as DB2, SQL Server, Oracle, IMS, Informix, Access, or Ingress.

entity instance

A term used in ER modeling to refer to a specific table row. Also known as an entity occurrence.

relationship

An association between entities.

object-oriented database management system (OODBMS)

Data management software used to manage data found within an object-oriented database model.

internal schema

Depicts a specific representation of an internal model, using the database constructs supported by the chosen database. (The internal model is the representation of a database as "seen" by the DBMS. In other words, the internal model requires a designer to match the conceptual model's characteristics and constraints to those of the selected implementation model.)

Connectivity

Describes the classification of the relationship between entities. Classifications include 1:1, 1:M, and M:N.

relational model

Developed by E. F. Codd (of IBM) in 1970, it represents a major breakthrough for users and designers because of its conceptual simplicity. The relational model, based on mathematical set theory, represents data as independent relations. Each relation (table) is conceptually represented as a matrix of intersecting rows and columns. The relations are related to each other through the sharing of common entity characteristics (values in columns).

one-to-one relationship (1:1)

In a 1:1 relationship, one entity instance is associated with only one instance of the related entity.

relation

In a relational database model, an entity set. Relations are implemented as tables. Relations (tables) are related to each other through the sharing of a common entity characteristic (value in a column).

entity set

In a relational model, refers to a grouping of related entities.

internal model

In database modeling, refers to a level of data abstraction that adapts the conceptual model to a specific DBMS model for implementation.

subschema

In the network model, the portion of the database "seen" by the application programs that produce the desired information from the data in the database.

method

In the object-oriented data model, a named set of instructions to perform an action. Methods represent real-world actions, and are invoked through messages.

Inheritance

In the object-oriented data model, the ability of an object to inherit the data structure and methods of the classes above it in the class hierarchy. See also class hierarchy.

hardware independence

Means that a model does not depend on the hardware used in the implementation of the model. Therefore, changes in the hardware will have no effect on the database design at the conceptual level.

business rule

Narrative descriptions of a policy, procedure, or principle within an organization. Examples: A pilot cannot be on duty for more than 10 hours during a 24-hour period. A professor may teach up to four classes during any one semester.

entity occurrence

See entity instance.

extended relational data model (ERDM)

Sometimes referred to as the enhanced entity relationship model; the result of adding more semantic constructs (entity supertypes, entity subtypes, and entity clustering) to the original entity relationship (ER) model.

external model

The application programmer's view of the data environment. Given its business focus, an external model works with a data subset of the global database schema.

semantic data model

The first of a series of data models that more closely represented the real world, modeling both data and their relationships in a single structure known as an object. The SDM, published in 1981, was developed by M. Hammer and D. McLeod.

Data Definition Language (DDL)

The language that allows a database administrator to define the database structure, schema, and subschema.

class hierarchy

The organization of classes in a hierarchical tree in which each parent class is a superclass and each child class is a subclass. See also inheritance.

External Schema

The specific representation of an external view; the end user's view of the data environment.

table

a (conceptual) matrix composed of intersecting rows (entities) and columns (attributes) that represent an entity set in the relational model. Also called relation.

object/relational database management system (O/RDBMS)

a DBMS based on the extended relational model (ERDM). The ERDM, championed by many relational database researchers, constitutes the relational model's response to theOODM. This model includes many of the object-oriented model's best features within an inherently simpler relational database structural environment.

attribute

a characteristic of an entity or object. Has a name and data type.

class

a collection of like objects with shared structure (attributes) and behavior (methods). A class encapsulates an object's data representation and a method's implementation. Classes are organized in a class hierarchy.

Schema

a logical grouping of database objects (tables, indexes, views, queries, etc.) that are related to each other. Usually, a schema belongs to a specific single user or application.

Crow's Foot notation

a representation of the entity relationship diagram using a three-pronged symbol to represent the "many" sides of the relationship.

data model

a representation, usually graphic, of a complex "real world" data structure. Data models are used in the database design phase of a database life cycle.

object

an abstract representation of a real-world entity that has a unique identity, embedded properties, and the ability to interact with other objects and with itself.

hierarchal model

no longer a major player in the current database market; impt. to know, however, because the basic concepts and characteristics form the basis for subsequent database development. The model is based on an "Upside-down" tree structure in which each record is called a segment. The top record is the root segment. Each segment has a 1:M relationship to the segment directly below it.

one-to-many relationship (1:M)

on entity instance is associated with many instances of the related entity.

many-to-many relationship (M:N)

one of three types of relationships (associations among two or more entities) in which one occurrence of an entity is associated with many occurrences of a related entity, and one occurrence of the related entity is associated with many occurrences of the first entity.

entitiy

something about which someone wants to store data; typically a person, a place, a thing, a concept, or an event.

data management language (DML)

the language (set of commands) that allows an end user to manipulate the data in the database. (SELECT, INSERT, UPDATE, DELETE, COMMIT, and ROLLBACK)

conceptual model

the output of the conceptual design process. The conceptual model provides a global view of an entire database. describes the main data objects, avoiding details.