Technical brief - OpenDocument Format

"The OpenDocument Format (ODF) is an open international standard that allows the exchange and retrieval of information in office documents.

ODF uses descriptive XML tags, so that large parts of an ODF document can be understood even without reading the specification.

ODF stores document content in a ZIP archive. Thus, unzipping an ODF file reveals XML streams, which then can be processed. The ZIP compression keeps the file size small without making the access difficult. Most programming and scripting languages, as well as build environments like Apache Ant, provide support for ZIP archives."

http://reddevnews.com/techbriefs/article.aspx?editorialsid=802