Base64 XML binary content

Question

I have to send binary data in XML and the standard way of doing that is using base64; however I have two options:

• store the binary into a xs:base64binary
• store the utf-8 encoded string representation of the base64 binary into a xs:string element

In the first case the schema reads:

 <xs:element name="Image" type="xs:base64Binary" />

In the second case the schema reads:

 <xs:element name="Image" type="xs:string" />

I suspect the first option is the more "correct", however it generates an XML that is bigger than the second option. The first element int the XML instance starts with "U1Vrc..." etc, the second one starts with "SUkqAAA.." etc.

Which one would be the most usual to see out there?

Answer 1

The best option is to not store binary data in the XML at all, send it separately and have the XML refer to the external data as needed. But if you have to store it in the XML directly, then base64Binary and hexBinary are the only built-in data types for binary data, but they are certainly not the only choice. There are other algorithms available that also encode data using alpha/numeric alphabets that are compatible with XML strings. Search around, or devise your own syntax that only encodes binary bytes that are restricted by XML and leave the rest unencoded.