Information Technology Reference
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ture, which makes it most suitable for top-down applications. Its main DBMS is
IMS by IBM Corporation. It is a record-based database and the users follow a hi-
erarchical sequence to access the database by default. However, the users can also
access the database directly by specifying the segment keys along the access paths.
Its main disadvantage is its implementation of m:n relationships in the conceptual
model. Data redundancy occurs as a result of the implementation.
The network database has a graphic data structure (i.e., a record can have multi-
ple input and multiple output). It has Set data structure that is used as pointer to link
the owner and member records. It has the best performance among the other data
models, but is also the less user-friendly model. Its main advantage is to implement
an m:n relationship among the records. IDMS is a main legacy network DBMS by
Computer Associates International Ltd.
The relational database is the most popular data model in the industry now. It is
very user friendly among all the other models. Its data structure is tables that link to
each other through foreign keys or composite keys. However, these keys may cause
data redundancy. Normalization is needed to eliminate anormalies. At present, SQL
is the standard DDL and DML for relational databases, and is also the most used
database language.
The object-oriented database is based on grouping related instances (i.e., objects)
into class. Its data structure is based on OID, an object identity that is generated as a
unique number by the system. OID is used as a pointer to link class objects together.
Its major advantages are increased productivity by inheritance and encapsulation.
Its major attraction is its ability in reengineering existing object-oriented database
systems for future enhancements, i.e., it is more flexible than the other data models.
It seems to take a more important role in the future to replace relational as the domi-
nant model. An example of object-oriented data model can be found in UniSQL.
As Internet computing becomes part of everyday life, the XML defined by W3C
committee has also been adopted as the data standard on the Internet. The XML is
an extension to HTML, and is programmable with XML schema and XML docu-
ment. The XML schema can be in the form of Document Type Definition (DTD) or
XSD. It has a hierarchical tree structure that focuses on the root element with other
elements under it. The DTD can also be visualized in the form of DTD Graph. Each
element represents a node in the graph, and the attributes describe the properties of
the element. The ID and IDREF must exist in pair with IDREF addressing to ID
in the XML document. The DTD Graph and XSD Graph can be used as an XML
conceptual schema for the design of an XML database.
The expert system is the core software for decision support system and informa-
tion systems. It plays the role of the experts by transferring expert knowledge into
a computer system. Technically, it can perform forward and backward chaining to
derive condition to conclusion, or conclusion from condition. As the information
age evolves to the knowledge age, so does information systems evolve to knowl-
edge based systems. The role of expert systems becomes more important since
knowledge-based systems and knowledge engineering becomes more popular in
the industry.
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