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Unit 8: Database System

are designed to use one of five database structures to provide simplistic access to information Notes
stored in databases. The five database structures are:
 the hierarchical model,
 the network model,
 the relational model,
 the multidimensional model, and
 the object model.

Inverted lists and other methods are also used. A given database management system may provide
one or more of the five models. The optimal structure depends on the natural organization of the
application's data, and on the application's requirements, which include transaction rate (speed),
reliability, maintainability, scalability and cost.
The hierarchical structure was used in early mainframe DBMS. Records’ relationships form a
treelike model. This structure is simple but nonflexible because the relationship is confined to a
one-to-many relationship. IBM’s IMS system and the RDM Mobile are examples of a hierarchical
database system with multiple hierarchies over the same data. RDM Mobile is a newly designed
embedded database for a mobile computer system. The hierarchical structure is used primarily
today for storing geographic information and file systems.
The network structure consists of more complex relationships. Unlike the hierarchical structure,
it can relate to many records and accesses them by following one of several paths. In other words,
this structure allows for many-to-many relationships.

The relational structure is the most commonly used today. It is used by mainframe, midrange
and microcomputer systems. It uses two-dimensional rows and columns to store data. The tables
of records can be connected by common key values. While working for IBM, E.F. Codd designed
this structure in 1970. The model is not easy for the end user to run queries with because it may
require a complex combination of many tables.
The multidimensional structure is similar to the relational model. The dimensions of the cube-like
model have data relating to elements in each cell. This structure gives a spreadsheet-like view of
data. This structure is easy to maintain because records are stored as fundamental attributes — in
the same way they are viewed — and the structure is easy to understand. Its high performance
has made it the most popular database structure when it comes to enabling online analytical
processing (OLAP).
The object oriented structure has the ability to handle graphics, pictures, voice and text, types
of data, without difficultly unlike the other database structures. This structure is popular for
multimedia Web-based applications. It was designed to work with object-oriented programming
languages such as Java.
The dominant model in use today is the ad hoc one embedded in SQL, despite the objections of
purists who believe this model is a corruption of the relational model since it violates several
fundamental principles for the sake of practicality and performance. Many DBMSs also support
the Open Database Connectivity API that supports a standard way for programmers to access
the DBMS.
Before the database management approach, organizations relied on file processing systems to
organize, store, and process data files. End users criticized file processing because the data is
stored in many different files and each organized in a different way. Each file was specialized
to be used with a specific application. File processing was bulky, costly and nonflexible when
it came to supplying needed data accurately and promptly. Data redundancy is an issue with

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