November 2013 Archive


Information Integration Via Semistructured Data

Unlike the other models we have discussed, data in the semistructured model is self-describing; the schema is attached to the data itself. That is, each node (except the root) has an arc or arcs entering it, and the labels on these arcs tell what role the node

XML and Its Data Model

XML (Extensible Markup Language) is a tag-based notation for "marking" documents, much similar to the familiar HTML or less familiar SGML. A document is nothing more nor less than a file of characters. However, while HMTL's tags talk about the presentation of the information

Document Type Definitions

In order for a computer to process XML documents automatically, there needs to be something like a schema for the documents. That is, we need to be told what tags can appear in a collection of documents and how tags can be nested. The description of the schema is given by a

Attribute Lists

There is a strong relationship between XML documents and semistructured data. Assume that for some pair of matching tags and in a document we make a node n. Then, if and are matching tags nested directly within the pair and (i.e., there are no

Relational Algebra

This section begins a study of database programming, that is, how the user can ask queries of the database and can change the contents of the database. Our focus is on the relational model, and especially on a notation for describing queries about the content of relations called

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