Page 188 - DCAP312_WEB_TECHNOLOGIES_II

Web Technologies-II

Notes 9.5.2 Distributed Database
Figure 9.5 shows how fragments of a corporate database are spread across remote locations.
Global organizations or enterprises with widespread domestic operations can benefit from
distributed databases. In such organizations computer development is also disseminated, with
processing done locally at each location. A distributed database gets fragmented into smaller
data sets. Normally, you would divide the database into data sets on the basis of usage. If a
fragment contains data that are most relevant to one location, then that data set is kept at that
location. At each location, a fragment of the enterprise data is placed based on the usage.
Each fragment of data at each position may be managed with the identical type of database
organization system. For example, you may run Oracle DBMS at every location. In that case,
you run your distributed database as a homogenous database. On the other hand, if you elect
to manage the data fragments at different locations with different DBMSs, then you run your
distributed database as a anthology of heterogeneous database systems. Assorted arrangement
provides extra flexibility. However, heterogeneous distribution is difficult to coordinate and
administer.

Figure 9.5: Distributed Database

Fragment
of
Fragment Enterprise
of Database
Enterprise
Database

Fragment
of
Enterprise
Database
Fragment
Fragment of
of Enterprise
Enterprise Database
Database

For global and spread-out Two categories:
organizations, centralized Homogeneous database
databases not economical.
Heterogeneous database
Enterprise data distributed
across multiple computer
systems.

9.6 Creating a Basic Object Model

The object model of Smalltalk is simple and uniform, everything is an object. However, this
uniformity can still be a source of problem for programmers used to other languages.
The Rules of the Model

The design of the object model is based on a set of simple rules that are applied uniformly.
The rules are the following ones:
Rule 1: Everything is an object that has some private data.

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