various characteristics of DBMS approach

1. Self-contained nature

      DBMS system contains data plus a full description of the data (called “metadata”) “metadata” is data about data - data formats, record structures, locations, how to access, indexes metadata is stored in a catalog and is used by DBMS software to know how to access the data. Contrast this with the file processing approach where application programs need to know the structure and format of records and data.

2. Program-data independence

      Data independence is immunity of application programs to changes in storage structures and access techniques. E.g. adding a new field, changing index structure, changing data format, In a DBMS environment these changes are reflected in the catalog. Applications aren’t affected. Traditional file processing programs would all have to

change, possibly substantially.

3. Data abstraction

      A DBMS provides users with a conceptual representation of data (for example, as objects with properties and inter-relationships). Storage details are hidden. Conceptual representation is provided in terms of a data model.

4. Support for multiple views

      DBMS may allow different users to see different “views” of the DB, according to the perspective each one requires. E.g. a subset of the data - For example; the people using the payroll system need not/should not see data about students and class schedules. E.g. data presented in a different form from the way it is stored - For example someone interested in student transcripts might get a view which is formed by combining information from separate files or tables.

5. Centralized control of the data resource

      The DBMS provides centralized control of data in an organization.

      This brings a number of advantages:

      (a) reduces redundancy

      (b) avoids inconsistencies

      (c) data can be shared

      (d) standards can be enforced

      (e) security restrictions can be applied

      (f) integrity can be maintained

a, b. Redundancy and Inconsistencies

      Redundancy is unnecessary duplication of data. For example if accounts department and registration department both keep student name, number and address.

      Redundancy wastes space and duplicates effort in maintaining the data.

      Redundancy also leads to inconsistency.

      Inconsistent data is data which contradicts itself - e.g. two different addresses for a given student number. Inconsistency cannot occur if data is represented by a single entry (i.e. if there is no redundancy).

      Controlled redundancy: Some redundancy may be desirable (for efficiency). A DBMS should be aware of it, and take care of propagating updates to all copies of a data item.

      This is an objective, not yet currently supported.

c. Sharing

      • Need concurrency control

      • Multiple user views

d. Standards

      E.g. data formats, record structures, naming, documentation

      International,   organizational, departmental ... standards

e. Security

      - restricting unauthorized access

      DBMS should perform security checks on all accesses.

f. Integrity

      Maintaining validity of data;

      e.g. employee numbers must be in some range

      e.g. every course must have an instructor

      e.g.. student number must be unique

      e.g. hours worked cannot be more than 150

      These things are expressed as constraints.

      DBMS should perform integrity checks on all updates. Currently DBMSs provide limited integrity checks.

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