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=Key-Value Pair Property Bag Extensiblity Mechanism=
==Introduction==
* Original RT request: https://rt.egi.eu/rt/Ticket/Display.html?id=3764 
* Simiar to the GLUE2 extensibility mechanim, the core GOCDB entities (NGIs, Sites, Services, ServiceGroups) will be extended so that they can define an optional set of custom key-value pairs. 
* In doing this, additional parameters could be supplied to the PI for selecting entities that define a particular set of properties. For example "select all Sites/Services that define the 'MPI=true' property."
* As an extensibility mechanism, we do not intend to impose any restrictions on the values of key-value pairs (other than max value length, e.g. 255 chars ). Key-value pair meaninings should be determined as a community folksonomy.

==PI Examples==
The URL query could be parameterised with a known GET request paramter (e.g. 'extensions') with a LDAP syntax query string for the value, eg: 
This extensions parameter allows you to supply an LDAP styled query to further filter your site and endpoint results. For example:

<pre>?method=get_site&extensions=(VO=Alice)</pre>

Will return all sites that define VO with a value of Alice. A wildcard could also be used:

<pre>?method=get_site&extensions=(VO=*)</pre>

Will return all sites that define VO as a key property with any value. Comma separated lists of values are also supported:

<pre>?method=get_service_endpoint&extensions=(CPU_HS01_HOUR=1,2,3,4,5)</pre>

This will return any service endpoints that define a CPU_HS01_HOUR with a value of 1, 2, 3, 4, or 5. Extensions also supports OR/AND operators. This can be used to search against multiple key values eg:

<pre>?method= get_service_endpoint&extensions=(AND(CPU_HS01_HOUR=1)(CPU_HS02_HOUR=2))</pre>

This will return endpoints that define both CPU_HS01_HOUR with a value or 1 and CPU_HS02_HOUR with a value of 2. The same query can also be performed with OR:

<pre>?method= get_service_endpoint&extensions=(OR(CPU_HS01_HOUR=1)(CPU_HS02_HOUR=2))</pre>

This can then be used to find sites or service endpoints that all define the same group of key values:

<pre>?method=get_site&extensions=(AND(VO=Alice,Atlas,CMS,LHCB))</pre>

The extensions parameter can also be used in conjunction with the existing parameters previously supported:

<pre>?method=get_site&extensions=(OR(VO=Alice,Atlas,CMS,LHCB))&scope=EGI&roc=NGI_UK</pre>

These are currently in testing and can be viewed on the GocDB test server:

https://gocdb-test.esc.rl.ac.uk/v5_pi/public/?method=get_site&extensions=(VO=*)

https://gocdb-test.esc.rl.ac.uk/v5_pi/public/?method=get_site&extensions=(AND(VO=Alice,LHCB))

https://gocdb-test.esc.rl.ac.uk/v5_pi/public/?method=get_site&extensions=(OR(VO=CMS,LHCB,Atlas,Alice))

https://gocdb-test.esc.rl.ac.uk/v5_pi/public/?method=get_service_endpoint&extensions=(CPU_HS01_HOUR=*)

https://gocdb-test.esc.rl.ac.uk/v5_pi/public/?method=get_service_endpoint&extensions=(OR(CPU_HS01_HOUR=*)(CPU_HS02_HOUR=5))

https://gocdb-test.esc.rl.ac.uk/v5_pi/public/?method=get_service_endpoint&extensions=(AND(CPU_HS01_HOUR=*)(CPU_HS02_HOUR=5))

https://gocdb-test.esc.rl.ac.uk/v5_pi/public/?method=get_service_endpoint&extensions=(CPU_HS01_HOUR=*)&sitename=RAL-LCG2


Note:
* The extent to which the ldap syntax query string would be supported will have to be explored. A simplified version including only exact pattern matches and simple wildcards may cover most use cases. 
* The property bags may only be applied to a subset of entities and PI queries.

==Sample PI XML Output==
<source lang="XML">
<?xml version="1.0" encoding="UTF-8"?>
<results>
   <results>
<SITE ID="259" PRIMARY_KEY="458G0" NAME="NGS-HECTOR">
<PRIMARY_KEY>458G0</PRIMARY_KEY>
<SHORT_NAME>NGS-HECTOR</SHORT_NAME>
<OFFICIAL_NAME>HeCTOR, UK National Supercomputing Service</OFFICIAL_NAME>
<SITE_DESCRIPTION>Pending</SITE_DESCRIPTION>
<GOCDB_PORTAL_URL>
https://127.0.0.1/DoctrineP/index.php?Page_Type=Site&ampid=259
</GOCDB_PORTAL_URL>
<HOME_URL>www.hector.ac.uk</HOME_URL>
<CONTACT_EMAIL>support@hector.ac.uk</CONTACT_EMAIL>
<CONTACT_TEL>0131-650 5029</CONTACT_TEL>
<COUNTRY_CODE>GB</COUNTRY_CODE>
<COUNTRY>United Kingdom</COUNTRY>
<ROC>NGI_UK</ROC>
<SUBGRID>NGS</SUBGRID>
<PRODUCTION_INFRASTRUCTURE>Production</PRODUCTION_INFRASTRUCTURE>
<CERTIFICATION_STATUS>Uncertified</CERTIFICATION_STATUS>
<TIMEZONE>UTC</TIMEZONE>
<CSIRT_EMAIL>helpdesk@hector.ac.uk</CSIRT_EMAIL>
<DOMAIN>
<DOMAIN_NAME>hector.ac.uk</DOMAIN_NAME>
</DOMAIN>
<EXTENSIONS>
<EXTENSION>
<LOCAL_ID>24</LOCAL_ID>
<KEY>VO</KEY>
<VALUE>LHCB</VALUE>
</EXTENSION>
<EXTENSION>
<LOCAL_ID>21</LOCAL_ID>
<KEY>VO</KEY>
<VALUE>Alice</VALUE>
</EXTENSION>
<EXTENSION>
<LOCAL_ID>22</LOCAL_ID>
<KEY>VO</KEY>
<VALUE>Atlas</VALUE>
</EXTENSION>
<EXTENSION>
<LOCAL_ID>23</LOCAL_ID>
<KEY>VO</KEY>
<VALUE>CMS</VALUE>
</EXTENSION>
</EXTENSIONS>
</SITE>

</results>
</source>

==Potential Use Cases==
A number of potential use cases have been reported (https://rt.egi.eu/rt/Ticket/Display.html?id=3764), including:
* Specifying service access protocol. 
* Defining custom monitoring parameters. 
* Defining custom functionality/capability flags supported by a service (this may be related to MPI in EGI requirements, see: https://documents.egi.eu/public/RetrieveFile?docid=1260&version=3&filename=VT-MPI_Report_v3_final.pdf and https://rt.egi.eu/rt/Ticket/Display.html?id=3396).

==Issues==
There is the potential for proliferation of key-value pairs that should instead be recorded in fields/properties as part of the data model.