$get operation helpers / enhancements

[Michael Schwartz <mike@gluu.org>]

XDI TC:

Continuing the discussion on filtering $get requests, please review the 
following proposals.

Any feedback ahead of time would also be appreciated.

- Mike




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$get operation
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1) Server MAY return $is$binary as literal value instead of binary


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Filter by arc type $literal, $relational, $contextual
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Types:

$literal, $contextual, $relational
Example 1 - returns ONLY literal xdi statements

@!1111$msg!e2bdc4de-f129-4d84-9009-3572c37b04d0$do/$get$literal/@!4444
Example 2 - returns relational and contextual xdi statements

@!1111$msg!e2bdc4de-f129-4d84-9009-3572c37b04d0$do/$get$relational$contextual/@!4444
Example 3 - NO sense filter because it returns all xdi statements, $get 
operation by default returns all xdi statements. Filter can be simply 
skipped.

@!1111$msg!e2bdc4de-f129-4d84-9009-3572c37b04d0$do/$get$relational$contextual$literal/@!4444

=======
$binary
=======

To force $get operation to return binaries.

Example:

@!1111$msg!e2bdc4de-f129-4d84-9009-3572c37b04d0$do/$get$binary/@!4444


=========
$onelevel
=========

$onelevel - returns only one level from target node of $get operation

If client wants to go deeper then 1 one level for example 2, then it 
should made 2 sequential calls.

Example:

@!1111$msg!e2bdc4de-f129-4d84-9009-3572c37b04d0$do/$get$onelevel/@!4444


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Filter Expression / Evaluation
==============================

In evaluation filter only string operations can be used.

Example:

@!1111$msg!e2bdc4de-f129-4d84-9009-3572c37b04d0$do/$get($and(context=*friends*)(rel=*yuriy*))/@!4444