Information Systems Reengineering, Integration and Normalization - Information Systems Reengineering, Integration and Normalization - page 8

tablished, but are based upon the matching of values in separate tables using a join
operation. This makes a relational database a more flexible system for inquiries
required. The predefined relationships of the hierarchical or network structures re-
quire a complex data definition language (DDL) and data manipulation language
(DML). Maintenance of these predefined relationships is difficult. In the relational
model, the DDL and DML are simpler and user-oriented, both having relatively
simple maintenance and physical storage conditions. Relational databases can pro-
vide better flexibility and data independence. Since an organization's need for in-
formation changes over time, and because having a relational database encourages
new uses, this flexibility of the relational model is highly desirable. Furthermore,
with the increasing use of Structured Query Language (SQL), the portability of ap-
plication programs using SQL as the DML is improved.
As database technologies evolve from hierarchical and network to relational and
object-oriented models, companies need guidelines on how to select a new database
system, and what should be done with their old and obsolete systems. The database
approach to information systems is a long-term investment. It requires a large-scale
commitment of an organization's resources in compatible hardware and software,
skilled personnel and management support. Accompanying costs include the educa-
tion and training of the personnel, conversion of existing applications, and the cre-
ation of new documentation. It is essential for an organization to fully appreciate, if
not understand, the problems of converting an existing, file-based system to a data-
base system, or upgrading an obsolete database system to a more user-friendly one,
and to accept the implications of this operation before they initiate such projects.
Before anything else, the management must decide whether or not the project is
feasible and if it matches the users' requirements. Costs, timetables, are performance
considerations, as well as the availability of expertise are also major concerns.
Management is concerned with a long-term corporate strategy. The database
selected must be consistent with the commitments of that corporate strategy. If the
organization does not have a corporate database, then it must be developed before
the conversion takes place. Selecting a database must be from the top-down. Data
flow diagrams, representing the organization's business functions, processes, and
activities, should be drawn up first. This should be followed by an entity-relation-
ship (ER) model (Chan, 1976 ), detailing the relationships of different business
information, and then finally by data modeling. If the ER model has a tree-like
structure, then a hierarchical model should be adopted; if the ER model shows
a network structure, a network model should be chosen. Otherwise, a relational
model should be chosen for a more user-friendly structure, or an object-oriented
model should be chosen for a universal structure. For Internet application, an XML
model is needed for e-commerce because XML has become the data standard of
Internet computing.
Although there are many theories of database design, many databases are found
to be unreliable, difficult to modify, and poor in performance. Database designers
face a complicated problem: how to arrange the data and programs on different
computers to obtain the intended performance, reliability, and availability. Leaving
this problem unsolved will restrict the success of database system reengineering.