Page 65 - DLIS408_INFORMATION_TECHNOLOGY-APPLICATIONSL SCIENCES

Information Technology and Application

Notes operational matters. It deals with storage layout of the conceptual level, provides supporting
storage-structures like indexes, to enhance performance, and occasionally stores data of
individual views (materialized views), calculated from generic data, if performance
justification exists for such redundancy. It balances all the external views’ performance
requirements, possibly conflicting, in attempt to optimize the overall database usage by
all its end-uses according to the database goals and priorities.
All the three levels are maintained and updated according to changing needs by database
administrators who often also participate in the database design.
The above three-level database architecture also relates to and being motivated by the concept of
Data independence which has been described for long time as a desired database property and was
one of the major initial driving forces of the Relational model. In the context of the above architecture
it means that changes made at a certain level do not affect definitions and software developed with
higher level interfaces, and is being incorporated at the higher level automatically. For example,
changes in the internal level do not affect application programs written using conceptual level
interfaces, which saves substantial change work that would be needed otherwise.
On one hand it provides a common view of the database, independent of different external view
structures, and on the other hand it is uncomplicated by details of how the data is stored or
managed (internal level). In principle every level, and even every external view, can be presented
by a different data model. In practice usually a given DBMS uses the same data model for both the
external and the conceptual levels (e.g., relational model). The internal level requires a different
level of detail and uses its own data structure types, typically different in nature from the structures
of the external and conceptual levels which are exposed to end-users (e.g., the data models above):
While the external and conceptual levels are focused on end-user applications, the concern of the
internal level is effective implementation details.

Task State the role of database architecure in Financial department of an organisation.

Access Control

Database access control deals with controlling who (a person or a certain computer program) is
allowed to access what information in the database. The information may comprise specific database
objects (e.g., record types, specific records, data structures), certain computations over certain
objects (e.g., query types, or specific queries), or utilizing specific access paths to the former (e.g.,
using specific indexes or other data structures to access information).
Database access controls are set by special an authorized (by the database owner) personnel that
uses dedicated protected security DBMS interfaces.

Database Design

Database design is done before building it to meet needs of end-users within a given application/
information-system that the database is intended to support. The database design defines the
needed data and data structures that such a database comprises. A design is typically carried out
according to the common three architectural levels of a database (see Database architecture above).
First, the conceptual level is designed, which defines the over-all picture/view of the database,
and reflects all the real-world elements (entities) the database intends to model, as well as the
relationships among them. On top of it the external level, various views of the database, are
designed according to (possibly completely different) needs of specific end-user types. More
external views can be added later. External views requirements may modify the design of the
conceptual level (i.e., add/remove entities and relationships), but usually a well designed conceptual

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