Database Systems Chapter 2: Data Models

Terminology and concepts covering data models, evolving database structures, business rules, and levels of data abstraction from Chapter 2.

Data Model

Relatively simple representations, often graphical, of complex real-world data structures.

Entity

Anything about which data are to be collected and stored.

Attribute

A characteristic of an entity.

Relationship

Describes an association among entities, which can be one-to-many ($1:M$), many-to-many ($M:N$), or one-to-one ($1:1$).

Constraint

A restriction placed on the data.

Business Rules

Descriptions of policies, procedures, or principles within a specific organization that describe characteristics of data as viewed by the company.

Hierarchical Model

A model developed in the 1960s with a basic logical structure represented by an upside-down "tree" containing levels or segments.

Network Model

A model created to represent complex data relationships effectively, allowing a record to have more than one parent.

Schema

The conceptual organization of the entire database as viewed by the database administrator.

Subschema

The portion of the database "seen" by the application programs.

Data Management Language (DML)

Defines the environment in which data can be managed.

Data Definition Language (DDL)

Enables the administrator to define the schema components.

Relational Model

Developed by E.F. Codd in 1970, it uses a matrix (relation) consisting of row and column intersections.

Tuple

A row in a relation (table) within the relational model.

Relational Database Management System (RDBMS)

Performed the same functions as the hierarchical model but hides complexity from the user and manages relational tables.

Entity Relationship Model (ERM)

Introduced by Chen in 1976, this model uses graphical representations to model database components.

Entity Set

A collection of like entities.

Connectivity

Labels used to classify the types of relationships in an Entity Relationship diagram.

Object-Oriented Data Model (OODM)

A model where data and relationships are contained in a single structure known as an object.

Inheritance

The concept where an object inherits the methods and attributes of its parent class.

Unified Modeling Language (UML)

A language based on OO concepts that uses diagrams and symbols to graphically model a system.

Extended Relational Data Model (ERDM)

A semantic data model that includes many features of the OO model and is often called an object/relational database management system (O/RDBMS).

Extensible Markup Language (XML)

The de facto standard protocol for data exchange among systems and Internet services.

External Model

The end users' view of the data environment, often represented by ER diagrams.

Conceptual Model

A global view of the entire database that integrates all external views into a single conceptual schema, independent of hardware and software.

Internal Model

A representation of the database as seen by the DBMS, mapping the conceptual model to specific database software.

Physical Model

The lowest level of abstraction, describing the way data are saved on storage media such as disks or tapes.

Logical Independence

The ability to change the internal model without affecting the conceptual model.

Physical Independence

The ability to change the physical model without affecting the internal model.