semantic web & XML

Question 1

semantic web definition

Answer 1

extension of the world wide web through standards by the world wide web consortium, the standards promote common data formats and exchange protocols on the web,

about meaning rather than syntax which is about structure

Question 2

proof and trust layers

Answer 2

proof layer- involves the actual deductive process as well as representation of proofs in web languages and proof validation
trust layer- emerge through the use of digital signatures and otherkinds of knowledge - certification, recommendation, security and the quality of information

Question 3

XML

Answer 3

extensible markup language, metalanguage used to represent and manipulate data elements. similar to HTML in structure but XML is concerned with the description and representation of data, rather than with the way it is displayed
documents have tags giving extra information about sections of the documents

Question 4

XML vs HTML

Answer 4

HTML tags describe how to render things on screen, XML tags describe what things are, HTML tags are designed for the human-computer interaction, wheras XML tags are designed for interaction between two computers, unlike HTML,XML tags tell you what the data means rather than how to display it

Question 5

why XML for databases

Answer 5

one of the main reasons that XML was developed was to allow the exchange of semi-structured documents, like invoices, order forms, applications.. over the internet. using a database system to store XML documents allows users to be able to better access information XML is also very flexible, data is maintained in a self-describing format to accommodate a variety of ever-evolving business needs

Question 6

XML database

Answer 6

database that stores XML documents, two major types of XML databases;
XML - enabled; these map all XML to a traditional database, accepting XML as input and rendering XML as output
native XML- the internal model of such databases depends on XML and uses XML documents as the fundamental unit of storage

Question 7

XML model vs relational model

Answer 7

XML data is hierarchical
* XML data is self-describing
* XML data has inherent
ordering
* An XML database contains
collections

• Relational data is
  represented in a model of
  logical relationships
• Relational data is not self-
  describing
• Relational data does not
  have inherent ordering
• A relational database
  contains tables

Question 8

relational model

Answer 8

order of rows is not guaranteed unless the ORDER BY clause is used in one or more columns, relations(tables), data is represented in n-ary relations. has a domain that represents a set of values. attributes (columns) strict schema, restrictive, the strict schema insures data integrity

Question 9

xml model

Answer 9

hierarchical format, data is represented in tree structures, nodes, relationships between the nodes.
schema provides flexibility, easily modified format

Question 10

XML document rules

Answer 10

XML documents must be well formatted, meaning that every opening
tag needs a closing tag (e.g. <Student> Marie </Student> )
* It allows users to define their own tags (unlike HTML)
* The XML tags need to be properly nested.
* The XML and xml tags are reserved for XML tags only.
* You can use <– XXX –> symbols for comments
* XML is case sensitive so, <Student> is not the same as <STUDENT>
* Two types of XML documents commonly used, Document Type
Definition (DTD) or an XML Schema Definitions (X</STUDENT></Student>

Question 11

document type definition

Answer 11

DTDs can be declared inline of the XML code or can reference
an external file
* It provides the composition of the database’s logical model and
defines the syntax rules or valid tags for each type of XML
document
* A DTD is a file that has a .dtd extension
* This file describes XML elements
* Example on next slide