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 This part is about how XML Documents can be stored and retrieved.

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Presentation on theme: " This part is about how XML Documents can be stored and retrieved."— Presentation transcript:

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2  This part is about how XML Documents can be stored and retrieved.

3  Several approaches to organizing the contents of XML documents to facilitate their subsequent querying and retrieval have been proposed. The following are the most common approaches.

4  A relation or object DBMS can be used to store whole XML documents as text fields within the DBMS records or objects.  This approaches cen be used if the DBMS has a special module for document processing, and would work for storing schemaless and document- centric XML documents.

5  The keyword indexing functions of the document processing module can be used to index and speed up search and retrieval of the documents

6  This approach would work for storing a collection of documents that follow a specific XML DTD or XML schema.  Because all the documents have the same structure, one can design a relational database to store the leaf data elements within the XML documents.

7  To be able to handle this it requires mapping algorithmsto design a database schema that is compatible with the XML document structure as specified in the XML schema to recreate the XML documents from the stored data.

8  A new type of database system based on the tree model could be desinged and implemented.  The system would include specialized indexing and would work for all types of XML documents.  By the way you can use compression techniques in this approach.

9  There are enormous amounts of data already stored in relational databases.  Parts of this data may need to be formatted as documents for exchanging or displaying over the Web

10  This approach would use a seperate middleware software layer to handle the conversions needed between the XML documents and teh relational database.

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12  In this part we focused on the last approach.  XML uses tree model to represent documents. When we add referential integrity constraints, a relational schema can be considered to be a graph structure.  Similarly also the ER model represents data using graphlike structures  There would be straightforward mappings between the ER and relational models.

13  So we can conceptually represent a relational database schema using the corresping ER schema.  Namely the issue is clarifying differences between tree and graph models. If we solve this also solve the problem of converting relational data to XML.

14  Objective: Creating application to extract XML documents for student course and grade information from University DB.

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16  To be able to do this we need COURSE, SECTION and STUDENT attributes.

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18  When we convert it to tree model we must select root. So in this example we can choose three different root.

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24  It is possible to have more complex subset with one or more cycles, indicating multiple relationships among entities  In this case it is more complex to decide how to create the document hierarchies.  Additional duplication of entities may be needed to represent the multiple relationships.

25  The way is to replicate the entity types involved in the cycles.

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27  It is necessary to create the correct query in SQL to extract the desired information for the XML document  Once the query is executed, its result must be structured from the flat relational form to the XML tree structure.


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