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Originally published 16 February 2006
In the days of operational transaction-processing systems, a service level agreement (SLA) was the agreement between the users and the IT department governing the expectations of the online environment. SLAs were created as a means of measuring and managing the service levels delivered to the end users for that environment. This agreement was a formal statement regarding proper service levels. Although it was somewhat like a contract, it was never a legally enforceable instrument.
SLAs covered two aspects of the online environment: response time and availability. Some SLAs were elaborate; some SLAs were very simple. A typical SLA would be:
Now that the world has embraced business intelligence and data warehousing, these environments also need SLAs. However, the SLAs that govern these environments are fundamentally different from the SLAs that govern the operational environment.
In order to understand the difference between the SLAs, consider what can be termed data warehouse velocity. (See Figure 1.)
Figure 1: Data Warehouse Velocity
Data warehouse velocity refers to the speed at which data moves through the business intelligence/data warehouse environment, from the initial entry into the operational environment, through ETL (extract, transform and load) and into the data warehouse, and finally to the data mart environment. Data warehouse velocity measures how quickly data becomes available throughout the data warehouse environment.
Note that velocity is a measure of availability. Some data marts are “pull” processes and only pull the data infrequently. Data may not flow for three months, for example. However, if needed, the data could be pulled on a daily basis. Therefore, actual velocity is different from potential velocity. Potential velocity refers to the speed that could be attained if the data warehouse operated on push processes, not pull processes.
The data warehouse SLAs rely on potential velocity. A typical business intelligence/data warehouse SLA would be:
Potential velocity – 48 hours from entry to data mart usage
One aspect of SLAs that remains fairly constant over the online and the business intelligence/data warehouse environment is that of availability. Both environments need a definition of when the system is available. It is response time and velocity that are very different from one environment to another.
Note that the flow of data may be for a data element that changes. The ETL process may alter the data, and the entry into the data mart environment also may alter the data. Therefore, the exact unit of data may not flow through the business intelligence/data warehouse environment at all. Instead, the mutated form of the data flows through the business intelligence/data warehouse environment.
The development of service level agreements for the business intelligence/data warehouse environment enables the IT department to provide a formal set of expectations for the end users.
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