Chapter 2

Front 1

Database schema

Back 1

The description of the database, which is specified during database design and is not expected to chage frequently

Front 2

Schema diagram

Back 2

Displaying schmas as diagrams

The diagram displays the strucutre of each record type but tnot the actual instances of records

Displays only some aspects of a schema,such as the names of record types and data items, and some types of constraints. Other aspects are not specified in the schema diagra.

Many types of constraints are not specified in schema diagrams.

Front 3

Populated

Back 3

The initial state of the database when the databasze us first populated or loaded with data. From then on, every time an update operation is applied to the database, we get another database state.

Front 4

Three-Schema Architecture

Back 4

1. Internal level
2. Conceptual level
3. External or View level

Front 5

Internal Level

Back 5

Describes the physical storage structure of the database

Uses a physical data model and describes the complete details of data storage and access paths for the database

Front 6

Conceptual Level

Back 6

Describes the structure of the whole database for a community of users

Hides the details of physical storage structures and concentrates on describing entities, data types, relationships, user operations, and constraints.

Front 7

External or View Level

Back 7

Describes the part of the database that a particular user group is interested in and hides the rest of the databse from that user group.

Front 8

Data Independence

Back 8

The capacity to chance the schema at one level of a database system without having to change the schema at the next higher level.

Front 9

Two Types:

Back 9

1. Logical data independence
2. Physcial data independence

Front 10

Logical data independence

Back 10

Capacity to change the conceptual schema without having to chage external schemas or application programs.

Front 11

Physical data independence

Back 11

The capacity to change the internal schema without having to change the conceptual schema

Front 12

Three-tier architecture

Back 12

Adds an intermediate layer between the client and the database server

Front 13

Application Server
or
Web Server

Back 13

Plays an intermediary role by storing business rules that are used to access data from the database server.

Accepts requests from the client,processes the request and sends database commands to the database server, and then acts as a conduit for passing processed data from the database server to the clients