1. Content Types: Markup and Multimedia

2. Introduction Markup languages use extra textual syntax to encode: –Formatting / display information –Structure information –Descriptive metadata –Semantic metadata Marks are often called tags –The act of adding markup is called tagging –Most markup languages use initial and ending tags surrounding the marked text

3. Standard Generalized Markup Language (SGML) Metalanguage for markup. –Includes rules for defining markup language –Use of SGML includes Description of structure of markup Text marked with tags Document Type Declaration (DTD) –Describes and names tags and how they are related –Comments used to express interpretation of tags (meaning, presentation, …)

4. SGML DTD Example <! ATTLIST e-mail idID#REQUIRED date_sentDATE#REQUIRED status (secret | public ) public > <! ATTLIST ref idIDREF#REQUIRED > <! ATTLIST (image | audio) id IDREF #REQUIRED >

5. SGML Example Pablo Neruda Federico Garcia Lorca Ernest Hemingway Picture of my house in Isla Gabriel Garcia Marquez Here are two photos. One is of the view (photo ). “photo1.gif” “photo2.jpg”

6. SGML Characteristics DTD provides ability to determine if a given document is well-formed. SGML generally does not specify presentation/appearance. Output specification standards: –DSSSL (Document Style Semantic Specification Language) –FOSI (Formatted Output Specification Instance)

7. HyperText Markup Language (HTML) Based on SGML –HTML DTD not explicitly referenced by documents HTML documents can have documents embedded within them –Images or audio –Frames with other HTML documents When programs are included, it is referred to as Dynamic HTML Strict HTML includes only non-presentational markup. –Cascade Style Sheets (CSS) used to define presentation In reality, presentational and structural markup are blended by HTML authoring applications.

8. HTML Limitations In contrast to SGML: –Users cannot specify their own tags or attributes. –No support for nested structures that can represent database schemas or object- oriented hierarchies. –No support for validation of document by consuming applications.

9. eXtensible Markup Language (XML) XML is a simplified subset of SGML –XML is a meta-language –XML designed for semantic markup that is both human and machine readable –No DTD is required –All tags must be closed Extensible Style sheet Language (XSL) –XML equivalent of CSS –Can be used to convert XML into HTML and CSS

10. Multimedia Lots of data file formats for non-textual data –Images BMP, GIF, JPEG (JPG), TIFF –Audio AU, MIDI, WAVE, MP3 –Video MPEG, AVI, QuickTime –Graphics / Virtual Environments CGM, VRML, OpenGL

11. Audio and Video Data files often have: –Header Indicates time granularity, number of channels, bits per channel Somewhat like a DTD –Data The signal Data may be compressed –Data may be in frequency domain rather than time domain –Data may be encoded as sequence of differences between consecutive time segments.