XML Database Program Knowing the Basic Concepts
As we know there are some basic similarities in an XML document and a relational database. Relational database consists of tables called relations in DBMS terminology and data is contained in table columns. In the same way an XML document consists of data in the form of elements. Databases have their schema as well as XML documents have XML schema or DTD.
An XML database
is the combination of both above mentioned data storing techniques i.e.
XML and relational databases and the motivation behind that is to devise
a technology where organizations can store their data in a format as simple
as XML and also an efficient mechanism like DBMS should be available for
manipulating, searching and retrieving the stored data. This is very crucial
in the case of companies where is need to deal with a huge amount of data.
So in an XML database, storage and exchange of data is done using XML based technology and data management is done by DBMS. An XML database can contain one or more XML documents and it possess all the properties of a relational database like oracle or mySQL. To understand a simple XML database, consider the following part of XML:
The above part of XML describes four elements: Student, Firstname, Lastname and Stream having values as Robert, Taylor and Science for the last three elements. Also there is an attribute of the element Student: rollno. Now for storing this as an XML database we have to store all the data contained in elements as well as all other components of document like tag names, attribute names.
So where XML database is concerned we are storing all the components of the document in the database. It should be noted here that if in place of XML database we have used traditional database for storing the data, we can only store the data contained in the elements. There could be a table having columns: student rollno, Firstname, Lastname and Stream. By now we have understood what the need of an XML database is and how it is different from a regular relational database.
Now we will discuss the types of XML database schemas which are generally used for creating relational databases to store the XML documents. First is coarse grained database. In this design whole XML document is kept in the database and no decomposition of document is done. This enables DBMS software to reference the XML document in less time and an easy and efficient management of data.
It is easy to exchange the document between two organizations as DBMS task is shortened to checking which records are unsent and then sending those records. Actually this style of storing XML document in a database is simple but it has disadvantages also.
As the whole document is stored, retrieval program has to parse the whole document, from beginning to end line by line in order to be able to use the data.
So the next XML database schema type is medium grained XML database which handles the problem of coarse grained type to some extent. In this style XML document is decomposed into different parts and each part is further stored in coarse grained style. A further refinement to the database schemas is fine grained XML database schema.
In this document is decomposed into its elements, attributes and their values. This makes manipulation and access of data elements easy for the retrieval program.
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