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ch27-XML Extensible Markup Language

ch27-XML Extensible Markup Language - Copyright 2007 Ramez...

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Slide 27- 1 Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe
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Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Chapter 27 XML: Extensible Markup Language
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Slide 27- 3 Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Chapter Outline Introduction Structured, Semi structured, and Unstructured Data. XML Hierarchical (Tree) Data Model. XML Documents, DTD, and XML Schema. XML Documents and Databases. XML Querying. XPath XQuery
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Slide 27- 4 Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Introduction Although HTML is widely used for formatting and structuring Web documents , it is not suitable for specifying structured data that is extracted from databases. A new language—namely XML (eXtended Markup Language) has emerged as the standard for structuring and exchanging data over the Web. XML can be used to provide more information about the structure and meaning of the data in the Web pages rather than just specifying how the Web pages are formatted for display on the screen. The formatting aspects are specified separately—for example, by using a formatting language such as XSL (eXtended Stylesheet Language).
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Slide 27- 5 Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Structured, Semi Structured and Unstructured Data Three characterizations: Structured Data Semi-Structured Data Unstructured Data Structured Data: Information stored in databases is known as structured data because it is represented in a strict format. The DBMS then checks to ensure that all data follows the structures and constraints specified in the schema.
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Slide 27- 6 Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Structured, Semi Structured and Unstructured Data (contd.) Semi-Structured Data: In some applications, data is collected in an ad-hoc manner before it is known how it will be stored and managed. This data may have a certain structure, but not all the information collected will have identical structure. This type of data is known as semi-structured data. In semi-structured data, the schema information is mixed in with the data values, since each data object can have different attributes that are not known in advance. Hence, this type of data is sometimes referred to as self-describing data.
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Slide 27- 7 Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Structured, Semi Structured and Unstructured Data (contd.) Unstructured Data: A third category is known as unstructured data, because there is very limited indication of the type of data. A typical example would be a text document that contains information embedded within it. Web pages in HTML that contain some data are considered as unstructured data.
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Slide 27- 8 Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Structured, Semi Structured and Unstructured Data (contd.) Semi-structured data may be displayed as a directed graph...
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