This month we’ll discuss one of the most difficult activities in our data warehouse design process – source system assessment. Often this activity is called "system of record" or "best source identification." In conjunction with requirements gathering and data quality assessment (the subject of next month’s column), we must identify not what source systems to draw data from, but how this is to be done. Fundamental activities to be completed are:

All but the first item necessitate changes to either the source system application code, supporting DBMS or file structure. If changes are made or required to the code or DBMS, you may end up impacting either the performance or availability of these systems. Therefore, the only practical solution (in most cases) is to access the entire source system’s DBMS through its mirror image copy, during off-line hours, or conduct the necessary extracts for comparison against the last load. We must also consider the capabilities and capacity of the DBMS and its database server in defining our data staging requirements for source system loading. We need to consider:

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