PDM Chapter 1: Databases and Database Design

ACID

denotes the four desirable properties of database transactions: Atomicity, Consistency, Isolation, and Durability.

Catalog

a repository for data definitions generated by the DDL compiler, integrity rules, metadata, and other information such as users, user groups, and statistics about data storage.

Conceptual data model

a high-level description of data items, characteristics, and relationships. Used for communication between information architect and business user to ensure data requirements are properly captured and modeled.

Data definition language (DDL)

language used by the database administrator to express the database’s external, logical, and internal data models.

Data independence

when changes in data definitions in one layer of the database architecture have minimal to no impact on the other layers.

Data manipulation language (DML)

used to retrieve, insert, delete, and modify data in a database. DML statements can be embedded in a general-purpose programming language, or entered through a front-end querying tool.

Database

a collection of related data items within a specific business process or problem setting stored on a computer system through the organization and management of the database management system.

Database approach

a data management approach in which all data are stored centrally and managed by a DBMS. Each application has access to the data it needs through the DBMS, resulting in fewer instances of duplicate data or data with errors.

Database management system (DBMS)

a software package consisting of several software modules used to define, create, use, and maintain a database.

Database model

The description of the database data at different levels of detail, specifying the data items, their characteristics and relationships, constraints, storage details, etc.

Database schema

different word for database model

Database system

the combination of a database and database management system

External data model

the subsets of the data items in the logical model, also called views, tailored toward the needs of specific applications or group of users.

File-based approach

a data management approach common in the early days of computing, in which every application stored its data in its own dedicated files, which resulted in multiple instances of duplicate data or data with errors.

Internal data model

a representation of a database’s physical storage details.

Internal layer

specifies how the data are stored or organized physically

Logical data independence

the ability to make changes to the conceptual/logical layer with minimal impact on the external layer.

Logical data model

the translation or mapping of the conceptual data model toward a specific implementation enviornment.

Metadata

the data definitions stored in the catalog of the DBMS.

Physical data independence

the ability to physically reorganize the data with minimal impact on the conceptual/logical or external layer.

Semi-structured data

data which have a certain structure, but the structure may be very irregular or highly volatile. Examples are individual users’ web pages on a large social media platform, or resume documents.

Structured data

data in which the individual characteristics of data items (such as the number, name, address, and email of a student) can be identified and formally specified.

Three-layer architecture

a description of how the underlying data models of a database are related. The three layers are external, conceptual/logical, and internal.

Unstructured data

data with no finer-grained components that have been formally specified. A long text document is an example.

View

a subset of the data items in the logical model tailored toward the needs of a specific application or group of users. Often called a virtual table in a relational setting.