Database Reference
In-Depth Information
3.7 Non-Relational Approaches
Prior to development of the relational model, the following approaches used to be employed:
•
Inverted List Approach: Exemplified by DATACOM/DB
•
Hierarchical Approach: Exemplified by Information Management
System (IMS) database and the Random Access Management
Information System (RAMIS)
•
Network Approach: Exemplified by Conference on Data Systems
Languages (CODASYL) initiative and Integrated Database
Management System (IDMS) initiative
The strengths of the relational approach when compared to these approaches are its
sound mathematical base, its flexibility, robustness, and simplicity.
In recent times, the
object oriented
(OO) model has been challenging the relational
model on performance and efficiency for certain scenarios. Nonetheless, we expect that
the two technologies will continue to peaceably coexist; huge investments have been
made in relational database systems, and it is not likely that these will be abandoned.
What is more likely to happen is that systems will be built based on relational databases,
with object oriented user interfaces superimposed.
3.8 Summary and Concluding Remarks
Let us summarize what we have covered in this very important chapter:
•
The relational database model is based on a number of
fundamental concepts relating to the following: entity, entity set,
relation, relationship, tuple, candidate key, primary key, alternate
key, foreign key, domain, cardinality, degree.
•
A domain is a named set of scalar values from which attribute
values are drawn.
•
A relation consists of a heading and a body. The heading consists
of atomic attributes defined on specific domains. The body
consists of a set of attribute-values pairs, where each attribute has
a value drawn from its domain.
•
In a database system, you are likely to find any combination of the
following types of relations: base relations, logical views, snapshots,
query results, intermediate results, and temporary relations.
•
A relational database system (RDBS) is a collection of time-varying
normalized relations, managed through an appropriate user
interface, and with desirable constraints and features that enhance
the effective, efficient management of the database.
