XDM Text Serialization

A proposal for text serialization of XDM for purposes of data interchange and interoperability.

Abstract

The XQuery 1.0 and XPath 2.0 Data Model (XDM) references a Serialization format for XDM. This format is "lossy" and does not reconstruct into the original XDM. In particular, for purposes of data interchange, the losses are severe; sequences are "normalized" and type information is discarded.
This proposal is to define a standard format for serializing XDM data for purposes of data interchange and interoperability preserving more of the XDM information.

Intent

The intent of this specification is to provide a standard format for interchange of data between XML tools which produce and consume XDM data. Examples of XML tools which produce or consume XDM data include XPath (2.0), XSLT , XQuery, but also include other tools such as XProc, xmlsh and countless custom written programs using the XDM data model.

In current implementations there is no standard model for XDM data either within the same environment and language, or across languages and environements. For example, suppose an XQuery operation produces a sequence and it is desired to provide that sequence as a parameter to XSLT transformation, there is no standardized way to exchange the data. In practice in order to accomplish this, either the same vendor tools must be used within the same language and process, or the results must be serialized in a proprietary format and reconstituted in the target using the same proprietary format. Even with the same vendors implementations interchange is not always easy due to differences in API layers, languages, or transferring data across process or machine boundaries.

This proposal provides for a standard serialization format so that XDM data can be interchanged across tools, vendors, languages, environments and machines.

Definitions

For the purposes of this document the following definitions apply

XDM Tool A program, module, function or API which can produce or consume XDM Data in some form.
XDM Consumer An XDM Tool which can consume (allow as input, arguments) XDM Data.
XDM Producer An XDM Tool which can produce XDM data (on output, return or output variables)
Environment An instance of the runtime of a single language with native language types, typically a single process.

Goals

This proposal expresses multiple goals, not all of which may be possible to achieve. The use cases describe concrete examples of many of the goals, while this summary provides the intent.

A standardized text representation of XDM data preserving as much of the XDM model as reasonable.
A representation that can be easily implemented using existing vendors XML technology.

Some purposes for which this standard could be used include

Exchange of XDM data between XDM Tools in different environments
Exchange of XDM data between XDM Tools from different vendors in the same environment
Exchange of XDM data between XDM Tools from the same vendor in the same environment where it is difficult to preserve the vendors native data structure
Exchange of XDM Data between XDM Tools and tools which are not XDM capable, or with limited XDM capability.
Provide a human readable output of XDM data
Output of XDM data from test cases using XDM Tools with the purposes of validation and compare
Standardization of a format for use in XML Pipeline Processors so that steps can be implemented by different vendors or in different languages.

Use Cases

Use cases are concrete examples that demonstrate the goals.

Use Case 1 Exchange of XDM data between XDM Tools in different environments
Use Case 2 Exchange of XDM data between XDM Tools from different vendors in the same environment
Use Case 3 Exchange of XDM data between XDM Tools from the same vendor in the same environment where it is difficult to preserve the vendors native data structure
Use Case 4 Exchange of XDM Data between XDM Tools and tools which are not XDM capible.
Use Case 5 Provide a human readable output of XDM data
Use Case 6 Output of XDM data from test cases using XDM Tools with the purposes of validation and compare
Use Case 7 Standardization of a format for use in XML Pipeline Processors so that steps can be implemented by different vendors or in different languages.

Serialization Format

Coming right after Use Cases !

XML Home : XDMSerialize

Revision [58]