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PEP#: 205
TITLE: PEP#205: CMPI CQL readme file

DESCRIPTION:

CMPI Providers in a nutshell
============================

Viktor Mihajlovski <mihajlov@de.ibm.com>
Nov 14th 2003

Pegasus 2.4 *NEWS*
------------------

The CMPI header files are being standardized and will be (possibly by the 
time you read this) frozen.  However, since the OpenPegasus 2.4 release is 
anticipated prior to the anticipated freezing of the CMPI standard, 
the OpenPegasus 2.4 release will not provide the CMPI header files as 
part of the OpenPegasus 2.4 SDK. 

They can be found within CVS and the source tarball. Visit
http://cvs.opengroup.org/cgi-bin/viewcvs.cgi/pegasus/src/Pegasus/Provider/CMPI/ to view the CMPI header files.

Build CMPI from sources
-----------------------

The Common Manageability Programming Interface (CMPI) has been integrated into
Pegasus as a pluggable provider manager.

CMPI must be enabled during Pegasus build.
For CMPI enablement, set the following environment variables prior to make:

   PEGASUS_ENABLE_CMPI_PROVIDER_MANAGER=1


Using CMPI
----------
If you plan to write your own CMPI providers you are kindly referred to the
WBEMSource homepage where the draft specification document for CMPI resides.
You can find at http://www.wbemsource.org/doc.tpl?CALLER=index.tpl&gdid=3712 .
If you are looking for samples you should have a look at the SBLIM project.
The packages prefixed by the string sblim-cmpi contain CMPI providers for
various classes. See http://www-124.ibm.com/developerworks/projects/sblim .


Using CQL with CMPI
-------------------

 To use CQL support for indications and exec query you will have to use
 the Pegasus/Provider/CMPI/cmpi_cql.h header file with one new function.
 You also  you need to define PEGASUS_USE_EXPERIMENTAL in your 
 code to take advantage of these CQL utility functions. The reason is that 
 the CMPI standard 1.0 is unclear on one thing:
 
   - CMNewSelectExp. One of arguments passed is a 'projection' array. The
     spec does not explain exactly what in such array. Implementation of
     CMPI that also implemented WQL put a string representation of the 
     properties, as "SystemName", "Hostname", etc. But that is not neccesarily
     the case with CQL, where you can have chained identifiers such as
     "CIM_OperatingSystem::SystemName". In other words, the CMPI standard
     needs to clarify this and to make the existing providers backward 
     supported, this utility function - CMPI_CQL_NewSelectExp is provided
     until the CMPI standard comes up with a conclusion on this.

  When the CMPI provides a resolution on these issues, this utility
  interface will be gone and unsupported.

  Questions and Answers:
Q1: Is the CMPI Specification really ambiguous or does it 
just not support CQL? If it's ambiguous should it be fixed 
before it goes final?

A1:. Page 96 of the CMPI review spec states (line 2899-2901): The *projection output argument is 
a pointer to a CMPIArray structure of CMPIString entries containing projection specification. 
It shall be set to NULL if no projection is defined.. To clarify any ambigiuity, an e-mail to the
 CMPI review group was sent, which would add the following: The projection specification is query 
language specific. Hence the entries format of the projection output array CMPIString might be 
different depending on the query language. Be sure to check the lang argument for the query language your 
provider will support. . To guard the provider from DMTF's CQL possible ways it can be represented in 
a string format, and since the CQL is experimental, the CMNewSelectExp will NOT support CQL. 
The CMPI_CQL_NewSelect will support both CQL and WQL.


AQ:What happens if an existing Provider is passed a CQL 
statement and issues a newSelectExp call?  Does it return 
an error?

A2: The error code CMPI_RC_ERR_QUERY_LANGUAGE_NOT_SUPPORTED would be set.


Q3: Both CMNewSelectExp and CMPI_CQL_NewSelectExp return a 
CMPISelectExp. Is there anyway to determine whether the 
CMPISelectExp represents a CQL or WQL expression?

A3:Not from the scope of the CMPISelectExp structure. Please note that the routine
 that would exercise the CMPISelectExp has a char *lang passed in as argument. 
This char *lang* can be used to easily determine what query language is used.



Registering CMPI providers with Pegasus
---------------------------------------

Once you have a CMPI provider library you want to register it with Pegasus.
How? Well it's almost the same as for C++ providers. The only difference is
that the Provider.Interface property must be set to "CMPI".

Here's an excerpt from the SBLIM Linux Computer System provider registration

// ===================================================================
// 	Linux_ComputerSystem
// ===================================================================


instance of PG_ProviderModule
{
   Name = "OSBase_ComputerSystemProviderModule";
   //The library name on disk
   Location = "cmpiOSBase_ComputerSystemProvider";
   Vendor = "SBLIM";
   Version = "1.2.2";
   InterfaceType = "CMPI";
   InterfaceVersion = "0.86.0";
};

instance of PG_Provider
{
   //The provider module as defined in PG_ProviderModule
   ProviderModuleName = "OSBase_ComputerSystemProviderModule";
   // The provider name as referenced in the code
   Name = "OSBase_ComputerSystemProvider";
};

instance of PG_ProviderCapabilities
{
   //The provider module as defined in PG_ProviderModule
   ProviderModuleName = "OSBase_ComputerSystemProviderModule";
   //The provider name as defined in PG_Provider
   ProviderName = "OSBase_ComputerSystemProvider";
   CapabilityID = "1";
   //Name of the CIM class as defined in the mof
   ClassName = "Linux_ComputerSystem";
   Namespaces = {"root/cimv2"};
   ProviderType = { 2,5 }; // Instance, Method
   SupportedProperties = NULL; // All properties
   SupportedMethods = NULL; // All methods
};