version 1.5, 2004/10/13 14:45:26
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version 1.6, 2005/03/01 06:18:02
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various classes. See http://www-124.ibm.com/developerworks/projects/sblim . | various classes. See http://www-124.ibm.com/developerworks/projects/sblim . |
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Using CQL with CMPI |
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To use CQL support for indications and exec query you will have to use |
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the Pegasus/Provider/CMPI/cmpi_cql.h header file with one new function. |
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You also you need to define PEGASUS_USE_EXPERIMENTAL in your |
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code to take advantage of these CQL utility functions. The reason is that |
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the CMPI standard 1.0 is unclear on one thing: |
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- CMNewSelectExp. One of arguments passed is a 'projection' array. The |
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spec does not explain exactly what in such array. Implementation of |
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CMPI that also implemented WQL put a string representation of the |
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properties, as "SystemName", "Hostname", etc. But that is not neccesarily |
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the case with CQL, where you can have chained identifiers such as |
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"CIM_OperatingSystem::SystemName". In other words, the CMPI standard |
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needs to clarify this and to make the existing providers backward |
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supported, this utility function - CMPI_CQL_NewSelectExp is provided |
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until the CMPI standard comes up with a conclusion on this. |
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When the CMPI provides a resolution on these issues, this utility |
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interface will be gone and unsupported. |
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Questions and Answers: |
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Q1: Is the CMPI Specification really ambiguous or does it |
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just not support CQL? If it's ambiguous should it be fixed |
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before it goes final? |
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A1:. Page 96 of the CMPI review spec states (line 2899-2901): The *projection output argument is |
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a pointer to a CMPIArray structure of CMPIString entries containing projection specification. |
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It shall be set to NULL if no projection is defined.. To clarify any ambigiuity, an e-mail to the |
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CMPI review group was sent, which would add the following: The projection specification is query |
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language specific. Hence the entries format of the projection output array CMPIString might be |
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different depending on the query language. Be sure to check the lang argument for the query language your |
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provider will support. . To guard the provider from DMTF's CQL possible ways it can be represented in |
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a string format, and since the CQL is experimental, the CMNewSelectExp will NOT support CQL. |
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The CMPI_CQL_NewSelect will support both CQL and WQL. |
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AQ:What happens if an existing Provider is passed a CQL |
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statement and issues a newSelectExp call? Does it return |
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an error? |
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A2: The error code CMPI_RC_ERR_QUERY_LANGUAGE_NOT_SUPPORTED would be set. |
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Q3: Both CMNewSelectExp and CMPI_CQL_NewSelectExp return a |
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CMPISelectExp. Is there anyway to determine whether the |
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CMPISelectExp represents a CQL or WQL expression? |
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A3:Not from the scope of the CMPISelectExp structure. Please note that the routine |
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that would exercise the CMPISelectExp has a char *lang passed in as argument. |
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This char *lang* can be used to easily determine what query language is used. |
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Registering CMPI providers with Pegasus | Registering CMPI providers with Pegasus |
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