From 956fb8b7908092f558502327fc71e56706f5e655 Mon Sep 17 00:00:00 2001
From: Dave Longley <dlongley@digitalbazaar.com>
Date: Sun, 24 Apr 2016 17:01:42 -0400
Subject: [PATCH] Add optimization for compacting keywords.

---
 jsonld.php | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/jsonld.php b/jsonld.php
index 4f4c21e..3f4f2af 100644
--- a/jsonld.php
+++ b/jsonld.php
@@ -4569,16 +4569,22 @@ class JsonLdProcessor {
       return $iri;
     }
 
-    // term is a keyword, default vocab to true
+    $inverse_ctx = $this->_getInverseContext($active_ctx);
+
     if(self::_isKeyword($iri)) {
-      $relative_to['vocab'] = true;
-    } else if(!isset($relative_to['vocab'])) {
+      // a keyword can only be compacted to simple alias
+      if(property_exists($inverse_ctx, $iri)) {
+        return $inverse_ctx->$iri->{'@none'}->{'@type'}->{'@none'};
+      }
+      return $iri;
+    }
+
+    if(!isset($relative_to['vocab'])) {
       $relative_to['vocab'] = false;
     }
 
     // use inverse context to pick a term if iri is relative to vocab
-    if($relative_to['vocab'] &&
-      property_exists($this->_getInverseContext($active_ctx), $iri)) {
+    if($relative_to['vocab'] && property_exists($inverse_ctx, $iri)) {
       $default_language = '@none';
       if(property_exists($active_ctx, '@language')) {
         $default_language = $active_ctx->{'@language'};