XtermIO - Rest API/JSON content Structure - Are there any Guides/Dictionaries?

Connecting to XtremIO clusters via Rest over https and receiving the JSON content back successfully. I will be creating histograms via RRDTool for IOPS, MBs, and Latency relative to block sizes as well as collecting and tracking rates and capacities of dedup, thin/oversubscription, physical space, physical used, logical used, allocated, etc. I am unsure of what some of the terms mean relative to the other data. An example of a Rest query on '/api/json/types/clusters/1' produces a content listing with some of the following:

HTTP/1.1 200 OK
Date: Tue, 03 Feb 2015 14:29:34 GMT
Server: TwistedWeb/8.2.0
Content-Type: application/json
Strict-Transport-Security: max-age=16070400;includeSubdomains
Transfer-Encoding: chunked

{
    "content": {
        "wr-bw-64kb": "8998",
..
        "ud-ssd-space-in-use": "2579321840",
..
        "space-in-use": "2579321840",
..
        "ud-ssd-space":  "16052147968",
..
     }
}

Just wondering things like - What does 'ud' stand for in the description of some of the content terms? So I was wondering if there is a dictionary relative to the data available from the JSON output of an XtremIO array? Are there different dictionaries relative to Code level running in the cluster?

Did not know if any of this information is available to customers?