Database Management Systems

Disadvantages of Database approach

- Can be costly to implement, additional hardware, software etc. - Can only run in certain operating environments - Because it is so different from the file-oriented approach, the database approach requires training users.

Advantages of Database approach

- No data redundancy, only stored once reducing storage costs - single update, only one place requiring one update. - current values, change to the info by any user yields current values to all users. - task-data independence

Disadvantages of File-oriented

- Redundant data and programs - Varying formats for storing the redundant data

Four primary elements of the database concept

- Users - the DBMS - the database administrator - the physical database

File-oriented processing

A specific data file was created for each application (flat-file)

Users

Can access the database in two ways: 1. through programs written by professional programs. The DBMS operates transparently to the users. 2. Through direct query. The DBMS uses its built-in query facility, which requires no formal programmer training to produce ad-hoc management reports

The database administrator

Controls sharing of database to users. Areas of duties: - database planning - database design - database implementation - database operation and maintenance - database change and growth

Data-oriented processing

Create a single data repository to support numerous applications (database)

Database approach

Pools data into a common database shared by all users which resolves problems - no data redundancy as all stored once - Users have access to all firm data, subject to authorization

The relational model

Portrays data in the form of two dimensional tables. Based on the relational algebra functions of restrict, project and join.

DML

Proprietary programming language that a particular DBMS uses to retrieve, process and store data to/from the database

Physical Database

Refers to the actual representation of the data on the storage media.

Association

Represented by a line connecting two entities. Described by a verb such as strips requests or receives.

DBMS

Stand between the user and the database. Commercial DBMS's actually consist of a database plus software to manage it and software to generate reports. Has special software to determine which users are authorized to access and deny unauthorized requests.

Cardinality

The degree of association between two entities. The number of possible occurrences in one table that are associated with a single occurence in a related table.

Database management system (DBMS)

a special software system that controls access to the database. Three conceptual models: - hierarchical model - network model - relational model

Flat-file approach

files were constructed with a particular application in mind and without any consideration for the needs of other applications or organizational sub-systems. Groups of users were almost exclusively concerned with their own problems. Secondly the data itself was stored to maximize efficiency for each particular application. Then due to the file structures being designed for one application it would not suit the requirements of other applications.