9.2 SOAP, DIME, and Binary Data

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So far we have seen that SOAP supports data from any XML schema, but what about binary data? The Direct Internet Message Encapsulation (DIME) specification defines a way of packaging up binary data into a SOAP message.

This is useful when confronted with the non-XML world, such as with electronic data interchange (EDI). Clearly, EDI documents can be converted to XML, and indeed BizTalk Server (see Chapter 4) has tools to do this precise transformation. The problem with the conversion process is that it will introduce an overhead since the data is serialized on one end and then deserialized at the other. If we only wanted to transfer the message, this would be rather time-consuming and inefficient, especially when the data has been compressed using some efficient binary compression algorithm. Another example would be images that could be converted to relatively large XML files, but why bother when you have a perfectly good JPEG or GIF image file?

Digital signing introduces further complexities. By its very nature, the binary data has been signed at origin, and if you interfere with the data to convert it into XML and back again for the SOAP message, the signature will be invalidated.

DIME is a mechanism that allows a SOAP message and an associated set of binary data to be transmitted as a single entity. A DIME message consists of one or more records, each with associated headers and data sections. The data in each of the records can vary in length, but the precise sequence of the records must be maintained. One of the benefits of DIME is that data can be 'chunked,' so that large amounts of data can be split into smaller segments for transmission, overcoming the limitations of some systems to cope with large data sets in one go.

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