2. Computers work with data represented by binary values 0, 1 represent possible “states” (values) of a switch (off and on) Operating systems and application software represent values differently A Word file storing information about this class will store the data differently than WordPad Working with Data
3. Text data uses common definitions for representing data Letter ‘a’ is 97 (110001 in binary) A text file with information about this class can be read and used by Word, Wordpad, Excel, Internet Explorer Using Text
4. “Markup” refers to the use of tags to describe data Data describing data is meta data Tags identify where data begins and ends, and has some information about that data Often referred to as “self describing” Standard Generalized Markup Language was created to offer universal standards for sharing and moving information Markup
5. HTML is an offshoot of SGML Designed to support display of data Not as complex – or as powerful – as SGML Text-based allows for reading and editing in many environments, applications Designed to be used explicitly with a browser Text values have fewer security issues than passing binary data What do all of those 0’s and 1’s represent? HTML
6. Extensible Markup Language fills the gap between display of HTML and complexity of SGML XML is compatible with rules of SGML XML isn’t a language XML is a set of standards about how to create a language to define and work with particular data To XML
7. Tags are used, similar to HTML Tags mark the beginning and ending of a value A tag must always have a close <name>Randy</name> OR <middle /> Tags are defined as needed No set of predefined tags as in HTML Tags typically aren’t about display Presentation is separate from the data, unlike HTML Using XML
8. XML is hierarchical Individual items in XML are elements An item may be a single value or group of values One element can belong to another Child and parent Similar to a one-to-many relationship Structure is called a ‘tree’ An item with children is called a branch An item with no children is a leaf XML Structure
9. An element can contain data An element can contain other elements An element can contain data and other elements Definition of elements for specific data make up a vocabulary Elements
10. Can define structure of data, independent of specific values Document type definitions(DTD’s) and schemas are used to create definitions Data isn’t part of a DTD or schema Can use definitions to test values Description of data can include validation Defining Elements
11. Every start tag must end Tags cannot overlap One tag can contain another Can have/must have one root element Must obey naming rules XML is case sensitive Whitespace is considered part of the data Not stripped out like for HTML Rules for Elements
