Database Reference
In-Depth Information
- Single user verses multi-user DBMS
- Centralised verses distributed DBMS
2.9.1 Object Oriented Data Model
An object is a logical grouping of related data and program logic that represents a real
world thing, such as a customer, employee, order, or product. Individual data items, such as
customer code and customer name, are called variables in the objectoriented model and are
stored within each object. a method is a piece of application program logic that operates on
a particular object and provides a finite function, such as checking a customer's credit limit
or updating a customer's address. Among the many differences between the object-orien-
ted model and the models already presented, the most significant is that variables may only
be accessed through methods. This property is called encapsulation.
The object-oriented model incorporates all of the characteristics of an objectoriented pro-
gramming language and essentially relegates the relational database to the status of a data
store. The fundamental idea here is that the database developer handles every aspect of
the database, including the sets of operations that manipulate the data in the database from
within the object-oriented database programming software.
2.9.2 Semantic DBMS
Semantic databases represent information as a collection of objects and relationships
between these objects. Data items related to objects can be of arbitrary size, multi-valued,
or missing entirely. This approach has been applied to various types of data, including sci-
entific and multi-media data.
This system should be useful for most typical database applications, as well as for special-
ized domains such as Earth Sciences.
Many database applications, e.g. those for Earth Sciences, have three essential needs:
(1) Strong
semantics
embedded in the database — to handle the complexity of information;
(2) Storage of multi-dimensional spatial, image, scientific, and other
non-conventional
data
; and
(3)
Very high performance
— to allow massive data flow.
2.9.3 Centralised DBMS
A centralized database has all its data on one place. As it is totally different from distributed
database which has data on different places. In centralized database as all the data reside
on one place so problem of bottle-neck can occur, and data availability is not efficient as
