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The main reason for the XML to Relational database integration is How to deliver business flexibility? It is to say that Can the information become a service? XML is used as it is recursive and flexible. Data structure definition validation, data separated from rendition, and human readable data.
Distributed systems are single (solo) components, in which components called services are put together. These components are used by the other applications, so the architecture should be such that it allows the components to use the applications in such a way that there is no effect to the architecture of the distributed system. At this point XML come to rescue. Since the past two-to-three years, XML is used for lingua translations for the any-to-any-data interchange and integration. XML is platform independent and Uni-code based syntax. It provides structured data and mark-up content. XML data is human readable and it only contains the information about the structure and the meaning of the data. XML can be helpful in solving the business problems that arise today.
The modelling and the data structure should be flexible in such a way that, there should be no effect on the performance. Relational database provides flexible and efficient management of the data for multiple usages. So in order to make this possible the relational data need to be transferred into XML, and the incoming XML data to be transformed into relational data. There are ways in which XML can be produced and stored with relational database systems.
Here the major parts are the Templates and the XML views in the middle-tier of the SQL server. Templates are the XML documents that allows and gives access to the queries and the update mechanism to the database which is (invisible) not visible to the user. Names elements are there which contains the query are processed by the template processor in the server and are returned to the database as its data in the form of XML document. XML views defined by the way in which they are mapped to the relational database table and the columns. Mapping is done to and from the database crating relationships in such a way that they express the outer join.
SQL provide different mode for how the serialization into XML can be done, with different level of complexity and XML capabilities. Modes are: auto, raw, and explicit. These modes are called the FOR XML. These modes help to bind the rows to elements and the columns to attributes. The goal for all the three FOR XML is that it should not slow down the non XML queries and the output should be streamlined and no effect on the sever side cache. To prevent impact to the database systems working and processing while it is generation the native sql queries, post-processing is done for serialization soon after the query is executed.
The auto mode applies a problem solving, learning and discovery technique on the returned data to determine nesting of the data. At this time it maps each row to an element while using the table alias as its name. This is determined by taking schema information provided by the SQL Server. Basically, the left to right appearance of a table alias in the SELECT clause determines the nesting. The columns placed in the hierarchy are grouped together even if they appear interspersed with columns of other aliases. XML looks at each row that arrives from the query processed and a new hierarchy level for the level where all the previous data is unchanged. This means that in Auto mode identical parents will be merged to one parent and that parents without children and parents with children without properties will be represented as parents with children without properties; children that are not directly following their parent will add a duplicate parent at the place where it reappears in the rowset stream.
The explicit mode generates arbitrary XML without any of the auto mode limitations, but the query should be explicitly authorized to return the rowset in a speciï¬Âc format. The format, is known as a universal table format. The explicit mode can generate arbitrary tree structured hierarchies, collapse or hoist hierarchical levels independently of the involved tables.