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Subject: JSON mapping choices

As mentioned in earlier emails and in the TC call today, there are several different “ad-hoc” schemes for mapping JSON to/from XML.  There is concern that if we pick one of these, it may be one that falls into obscurity as some other scheme picks up in popularity and ubiquity.


The advantages of picking an existing mapping scheme are

1.       We don’t have to define a scheme ourselves

2.       We can take advantage of existing tools to perform JSON/XML transforms.


Are there any other advantages of picking an existing mapping scheme?  I think most clients will be more interested that the JSON we define faithfully represents XACML notions and is easy to use and less concerned about the wire format or tool chain.


If we define our own mapping scheme, we can produce something that is a more natural fit for XACML notions and structure than a more generic scheme. As mentioned on the call, the generic schemes have to deal with the full extent of XML _expression_. We don’t need to represent all of XML, we only need to represent XACML notions in a way that can be transformed in and out of XML. We can look to existing schemes for inspiration but not be bound by them.


The main caveat is then tooling – making sure that it is easy for implementations to transform XACML XML to JSON and back.


I believe a transform from XACML XML to whatever JSON we determine can be defined using XSLT.  I don’t think XSLT is well suited to transform JSON to XML. That transform is probably best defined as a _javascript_ function that takes the JSON object tree and serializes to XML text.  Both of these transforms could be defined by the XACML TC and provided in the XACML JSON profile.  A reference implementation, if you will.


While using an existing pre-baked mapping scheme is attractive as a least-effort solution, I think the XACML community will be better served by defining our own mapping scheme using existing transform tools such as XSLT. 




Danny Thorpe

Product Architect | | Quest Software - Now including the people and products of BiTKOO | www.quest.com


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