Chapter 26 xml and Internet Databases Outline

Chapter 26

• XML and Internet Databases

Outline

• Structured, Semistructured, & Unstructured Data
• XML Hierarchical Data Model
• XML Document, DTD, & XML Schema
• XML Documents & Databases
• XML Querying

Structured vs Semistructured Data

• Structured Data:
• e.g., information stored in databases; all records have the same format as defined in the relational schema
• Semistructured data may have a certain structure but no all the information collected will have identical structure.

FIGURE 26.1 Representing semistructured data as a graph.

FIGURE 26.2 Part of an HTML document representing unstructured data (c.f., the company database schema)

XML Hierarchical (Tree) Data Model

• Problem with HTML document:
• Difficult to interpret automatically by programs because they do not include schema information about the type of data in the documents
• Inappropriate as intermediate Web documents to be exchanged among various computer sites
• Solution  XML documents
• Two main structuring concepts: elements, attributes
• c.f., In XML, tag names are defined to describe the meaning of the data elements, rather than to describe how the text is to be displayed (as in HTML).

FIGURE 26.3 A complex XML element called
.

• Correction:
  

• Complex elements:
  ,
  ,
• Simple elements: , , , …

• Standalone=“yes”
• - schemaless

XML Documents, DTD, and XML Schema

• A well-formed XML document is one that follows a few conditions.
• Start with an XML declaration (version, …)
• Tree model
• A single root element
• Matching start and end tags for an element must be within the tags of the parent element
• Syntactically correct