Signature schema documents, pre-defined in a query language, provide one or more instructions for application by an engine to transcode web pages of respective web sites. The instructions identify a web page family for the web page and extract a subset of data from the web page using one or more signatures previously identified within web pages of the same web page family (e.g. in accordance with a shared template for each family) of the web site. The instructions may include one or more directional references relative to the signatures to locate and extract the subset of data within the web page. Signatures may comprise text strings within the code of the web page and the directional references indicate positions of respective data relative to the location of the text strings. Transcoding may facilitate use of e-commerce web sites by wireless mobile devices.