<P> The HTML format used to define web pages allows for the inclusion of a variety of types of metadata, from basic descriptive text, dates and keywords to further advanced metadata schemes such as the Dublin Core, e-GMS, and AGLS standards . Pages can also be geotagged with coordinates . Metadata may be included in the page's header or in a separate file . Microformats allow metadata to be added to on - page data in a way that regular web users do not see, but computers, web crawlers and search engines can readily access . Many search engines are cautious about using metadata in their ranking algorithms due to exploitation of metadata and the practice of search engine optimization, SEO, to improve rankings . See Meta element article for further discussion . This cautious attitude may be justified as people, according to Doctorow, are not executing care and diligence when creating their own metadata and that metadata is part of a competitive environment where the metadata is used to promote the metadata creators own purposes . Studies show that search engines respond to web pages with metadata implementations, and Google has an announcement on its site showing the meta tags that its search engine understands . Enterprise search startup Swiftype recognizes metadata as a relevance signal that webmasters can implement for their website - specific search engine, even releasing their own extension, known as Meta Tags 2 . </P> <P> In broadcast industry, metadata is linked to audio and video broadcast media to: </P> <Ul> <Li> identify the media: clip or playlist names, duration, timecode, etc . </Li> <Li> describe the content: notes regarding the quality of video content, rating, description (for example, during a sport event, keywords like goal, red card will be associated to some clips) </Li> <Li> classify media: metadata allows producers to sort the media or to easily and quickly find a video content (a TV news could urgently need some archive content for a subject). For example, the BBC have a large subject classification system, Lonclass, a customized version of the more general - purpose Universal Decimal Classification . </Li> </Ul> <Li> identify the media: clip or playlist names, duration, timecode, etc . </Li>

Which of the following xml file extensions is for files that provide data scheme information