Compressing XML—Part I, Writing WBXML

ireless Binary XML (WBXML) is a compact representation of XML and is part of the presentation logic in Wireless Application Protocol (WAP). WBXML significantly improves the efficiency of transmitting XML over narrow bandwidth networks, where data size is of paramount importance.

Although WBXML was originally meant for wireless networks, it's suitable for more than wireless applications. Conventional web applications can also take advantage of WBXML's ability to carry the same information as that of its XML counterpart, but in a reduced size. With the advent of tools that can work directly with WBXML, there is no need to convert WBXML to XML before using it. You can generate SAX events directly from WBXML and even load a WBXML tree (DOM) in memory without converting it to XML.

WBXML is particularly useful in Electronic Data Interchange applications, where applications exchange huge volumes of XML data over the Internet. As an example, consider a database synchronization scenario, where proprietary formats are already converging to an open XML based grammar called "SyncML". SyncML supports all the familiar database synchronization operations (such as add, delete, copy, search, etc.) and requires only the simple exchange of SyncML files over the Internet. After interested parties have successfully exchanged SyncML files, back-end tools automatically synchronize their data stores. Hence database synchronization becomes a simple exchange of XML files. Unfortunately, SyncML files are often large, which leads back to WBXML—you can improve the efficiency of SyncML file exchanges by reducing their size, and you can do that by representing them in WBXML format.