13. A computer program product comprising: a computer-usable storage medium having computer-usable program code stored thereon that, when executed by a system comprising a processor and a memory, causes the system to perform a method of processing an Extensible Markup Language (XML) document, the method comprising: loading, via the processor, an execution plan into a virtual machine, wherein the execution plan represents an XML schema and specifies a hierarchy of XML components, and wherein the virtual machine comprises a plurality of dedicated XML processing functions specifically corresponding to the XML components specified by the XML schema; selectively invoking, via the processor, the XML processing functions available within the virtual machine according to the execution plan, wherein the XML processing functions operate upon an XML document; and outputting, via the processor, an indication of whether the XML document is valid according to the XML processing functions.
13. A computer program product comprising: a computer-usable storage medium having computer-usable program code stored thereon that, when executed by a system comprising a processor and a memory, causes the system to perform a method of processing an Extensible Markup Language (XML) document, the method comprising: loading, via the processor, an execution plan into a virtual machine, wherein the execution plan represents an XML schema and specifies a hierarchy of XML components, and wherein the virtual machine comprises a plurality of dedicated XML processing functions specifically corresponding to the XML components specified by the XML schema; selectively invoking, via the processor, the XML processing functions available within the virtual machine according to the execution plan, wherein the XML processing functions operate upon an XML document; and outputting, via the processor, an indication of whether the XML document is valid according to the XML processing functions. 18. The computer program product of claim 13 , wherein selectively invoking XML processing functions further comprises selecting an XML processing function that counts a number of occurrences of a component in the XML document.