Startup Updates

Data base systems today are essential to everyone business.Whenever you visit a major website Google,Yahoo,Amazon.com,or thousands of smaller sites that provide information there is a database behind the scenes serving up the information you request.Corporation maintain all their important records in the databases.Databases are likewise found at the core of many scientific investigations.They represent the data gathered by the astronomers,by investigations of the human genome and by biochemists exploring properties of proteins,among many other scientific activities.

             The power of data bases comes from a body of knowledge and technology that has developed over several decades and is embodied in specialized software called a database management system,or DBMS,or more colloquially a "database system".A database is a powerful tool creating and managing large amounts of data efficiently and allowing it to persist over long periods of time,safely .These systems are among the most complex types of software available.

What is a database?In essence a database is nothing more than a collection of information that exists over along period of time,often many years .In common parlance ,the term database refers to collection of data that is managed by a DBMS.The DBMS is expected to:

*Allow users to create new databases and specify their schemes

*Give users the ability to query the data

*Support the storage of very large amount of data many tera bytes or more over a long period of time ,allowing efficient access to the data for quires and database modifications.

*Enable durability the recovery of the database in the face of failure errors of many kinds,or intentional misuse.

*Control access to data from many users at once without  allowing unexpected interactions among users and without actions on the data to be performed partially but not completely.

The first commercial database management systems appeared in the late 1960's .These systems evolved from file systems ,which provide some of item above file systems store data over a long period of time ,and they allow the of large amounts of storage data.However,file systems do not generally guarantee that data cannot be lost if it is backed up and they don't support efficient access to data items whose location in a particular file is not known.

         Further,file systems do not directly support item a query language for the data in files .Their support for a scheme for data is limited to the creation of directory structures for files.Item is not always supported by file systems;you can lose data that has not been backed up.Finally ,file systems do not satisfy .While they allow concurrent access to files by several users or processes, a file system generally will not prevent situations such as two users modifying the same file at about the same time ,so the changes made by user fail to appear in the file.

 The First important applications of DBMS's were ones where data was composed of many small items and many quires or modifications were made 

Examples of these applications are;

*Banking system; maintaining accounts and making sure that systems failures do not cause money to disappear.

*Airline reservation systems these,like banking systems,require assurance that data will not be lost,and they must accept very large volumes of small by customers.

*Corporate record keeping;employment and taxes records,inventories,sales records,and a great variety of the other types of information ,much of of critical.

The early DBMS's required the programmer to visualise data much as it stored.These database systems used several different data models for describing the structure of the information a database,chief among them the "hierarchical" or tree based model and the graph based "network" model.The latter was standardized in the late 1960's through a report of CODASYL.

 A problem with early models and systems was that they did not support
high level query language had statements that allowed the user to jump from data elements.There was considerable effort needed to write such programs,even for every simple queries.

Following a famous paper written by Ted codd in 1970's,database systems changed significantly .  Codd proposed that database systems should present the user with a view of data organized be a complex data structure that allowed rapid response to a variety of queries .But unlike the programmers for earlier database system,the programmer of a relational system would not be concerned with the storage structure .Queries could be expressed in a very high level language,which greatly increased the efficiency of database programmers .SOL is the most important query language based on the relational model.
     By 1990,relational database systems were the norm.Yet the database field continue to evolve and new issues and approaches to the management of data surface regularly .Object oriented features have infiltrate the relational model.Some of the largest databases of this section ,we shall consider some of the modern trends in database systems.

     Originally DBMS's were large ,expensive software systems running too large computers .The size was necessary ,because to store a gigabyte of data required a large computers,Today ,hundreds of gigabytes fit on a single disk ,and it is quite feasible to run a DBMS on a personal computer.Thus database systems based on the relational model have become available for even very small machines,and they are beginning to appear as common tool for computer applications,much as spread sheets and word processors did before them.

Another important trend is the use of documents,Often tagged using XML .Large collections of small documents can   serve as a database , and the methods of querying and manipulating them are different from these used in relational systems.

On the other , a gigabyte is not that much any more.Corporate databases routinely store tera bytes.Yet there many databases that store petabytes of data and serve it all to users.Some important examples.

* Google holds petabytes of data gleaned from its crawl of the Web.This data is not held in a traditional DBMS,but in specialised structures optimised for search engine queries.

*satellites send down petabytes of information for storage in specialised systems.

*And if still pictures consume apace ,movies consume much more.