by Dinesh Thakur

A simple, flat-file database has only a single table, which means it has one set of records with fields. Each record within the table contains the same fields with the same type of information in each field, although of course the specific information you enter into each separate field is different. For instance, you might have a "Last Name" field on every record, but the actual last name on each record is different.



 
by Dinesh Thakur

The storing information in a data warehouse does not provide the benefits an organization is seeking. To realize the value of a data warehouse, it is necessary to extract the knowledge hidden within the warehouse. However, as the amount and complexity of the data in a data warehouse grows, it becomes increasingly difficult, if not impossible, for business analysts to identify trends and relationships in the data using simple query and reporting tools.



 
by Dinesh Thakur

Online Analytical Processing is used to answer the complex queries posted on data warehouse. In order to solve the queries of nature 'who?' and 'what?' we can use the simple tools but to answer the advanced queries like 'what if?' and 'why?', we require special tool that can support online analytical processing (OLAP).

 
by Dinesh Thakur

There are the three fundamentals components that are supported by data warehouse as shown in figure. These are:

 

• Load Manager

• Warehouse Manager

• Data Access Manger

 
by Dinesh Thakur

A Database Systems have been used traditionally for online transaction processing (OLTP). OLTP systems are designed to maximize the transaction processing capacity It is commonly used in clerical data processing tasks, structured repetitive tasks, read update a few records. In OLTP isolation, recovery and integrity are critical. It is based on operational systems.

 
by Dinesh Thakur

Today, multinational companies and large organizations have operations in many places within their origin country and other parts of the world. Each place of operations may generate large volume of data. For example, insurance companies may have data from thousands of local and external branches large retail chains have data from hundreds or thousands of stores and so on. Corporate decision maker require access of information from all such sources.



 
by Dinesh Thakur

The acronym DBTG refers to the Data Base Task Group of the Conference on Data Systems Languages (CODASYL), the group responsible for standardization of the programming language COBOL. The DBTG final report appeared in Apri1971, it introduced a new distinct and self-contained language. The DBTG is intended to meet the requirements of many distinct programming languages, not just COBOL, the user in a DBTG system is considered to be an ordinary application programmer and the language therefore is not biased toward any single specific programming language.

 
by Dinesh Thakur

Relational DBMSs are currently the dominant database technology. The OODBMS has also become the favored system for financial and telecommunications applications. Although the OODBMS market is still same. The OODBMS continues to find new application areas, such as the World Wide Web. Some industry analysts expect the market for the OODBMSs to grow at over 50% per year, a rate faster than the total database market.

 
by Dinesh Thakur

The lack of standard definition and framework for an OODBMS led to the design of first Object-Oriented Database System manifesto that was published in the Proceedings of the

First International Conference on Deductive and Object-Oriented Databases, Kyoto, Japan, December 1989. The manifesto included a set of features that a DBMS must· have to be referred as an OODBMS. The features framed were subdivided in three categories:



 
by Dinesh Thakur

Object Oriented Database (OODB) provides all the facilities associated with object oriented paradigm. It enables us to create classes, organize objects, structure an inheritance hierarchy and call methods of other classes. Besides these, it also provides the facilities associated with standard database systems. However, object oriented database systems have not yet replaced the RDBMS in commercial business applications.

 
by Dinesh Thakur

The definition of and DDBMS defines that the system should make the distribution transparent to the user. Transparent hides implementation details from the user. For example, in a centralized DBMS, data independence is a form of transparency it hides changes in the definition and organization of the data from the user. A DDBMS may provide a various· levels of transparency. However, they all participate in the same overall objective: to make the use of the distributed database, equivalent to that of a centralized database.



 
by Dinesh Thakur

Data can be stored in different computers by fragmenting the whole database into several pieces called fragments. Each piece is stored at a different site.

Fragments are logical data units stored at various sites in a distributed database system.



 
by Dinesh Thakur

Data Replication is the process of storing data in more than one site or node. This is necessary for improving the availability of data. There can be full replication, in which a copy of the whole database is stored at every site. There can also be partial replication, in which case, some fragment (important frequently· used fragments) of the database are replicated and others are not replicated. There are a number of advantages and disadvantages to replication.

 
by Dinesh Thakur

Function of a DDBMS

We expect a DDBMS to have at least the functionality for a centralized DBMS. In addition, we expect a DDBMS to have the following functionality:



 
by Dinesh Thakur

A DDBMS may be classified as homogeneous or heterogeneous. In a homogeneous system, all sites use the same DBMS product. In a heterogeneous system, sites may run different DBMS products, which need not be based on the same underlying data model, and so the system may be composed of relational, network, hierarchical and object-oriented DBMSs.



 
by Dinesh Thakur

The distribution of data and applications has potential advantages over traditional centralized database systems. Unfortunately, there are also disadvantages; in this section we review the advantages and disadvantages of DDBMS.

 
by Dinesh Thakur

"A logically interrelated collection of shared data (and a description of this data) physically distributed over a computer network."



 
by Dinesh Thakur

In-order to recover the system after these failures we need to identify the failure modes of those devices used for storage of data. Next, we must consider how these failure modes affect the contents of the database. Then we can propose the recovery algorithms to recover the database. Every Recovery algorithm performs two types of actions. These are:

 
by Dinesh Thakur

There are many different types of failure that can affect database processing, each of which has to be dealt with in a different manner. Some failures affect main memory only, while others involve non-volatile (secondary) storage. Among the causes of failure are:



 
by Dinesh Thakur

A DBMS can use encryption to protect information in certain situations where the normal security mechanisms of the DBMS are not adequate. For example, an intruder may steal tapes containing some data or tap a communication line. By storing and transmitting data in an encrypted form, the DBMS ensures that such stolen data is not intelligible to the intruder. Thus, encryption is a technique to provide privacy of data.



 
by Dinesh Thakur

Authorization is permission given "to user, program, or process to access an object or set of objects. The type of data access granted to a user can be read-only, or read and write. Privileges specify the type of Data Manipulation Language (DML) operations like SELECT, INSERT, UPDATE, DELETE, etc., which the user can perform upon data.

 
by Dinesh Thakur

The preservation of the integrity of a database system is concerned with the maintenance of the correctness and consistency of the data In a multi-user database environment this is a major task, since integrity violations may arise from many different sources, such as typing errors by data entry clerks, logical errors in application programs, or errors in system software which result in data corruption.

 
by Dinesh Thakur

Security is an important issue in database management because information stored in a database is very valuable and many time, very sensitive commodity. So the data in a database management system need to be protected from abuse and should be protected from unauthorized access and updates. It is popular belief that hackers cause most security breaches, but in reality 80% of data loss is to insiders.