On-Line Analytical Processing
... based on relationships. The OLAP Server may either physically stage the processed multi-dimensional information to deliver consistent and rapid response times to end users, or it may populate its data structures in real-time from relational or other databases, or offer a choice of both1. Data Warehouse A data warehouse is a subject oriented, integrated, non volatile, time variant collection of data. The data warehouse contains atomic level data and summarized data specifically structured for querying and reporting. Data Warehousing is an enterprise-wide implementation that replicates data from the same publication table on different servers/platforms to a single subscription table. This implementation effectively consolidates data from multiple sources2. A data warehouse is a repository storing integrated information for efficient querying and analysis. Information is extracted from various sources as it is generated or updated. The information is then translated into a common data model and integrated with exisiting data at the warehouse. When a user query is submitted to the warehouse, the needed information is already there, with inconsistencies and differences already resolved. This makes it much easier and more efficient to run queries over data that originally came from different sources. Key advantages of data warehousing include: • Since query execution does not involve data translation and communication with remote sources, complex queries can be executed easily and efficiently. • End users can use a single data model and query language. • Information sources may be unreliable and may purge data. On the other hand, information at the warehouse is under the control of the warehouse users; it can be stored safely and reliably for as long as necessary. Data Mart A data mart is a repository of data gathered from operational data and other sources that is designed to serve a particular community of knowledge workers. The data may come from an enterprise-wide database or data warehouse or be more specialized. The emphasis of a data mart is on meeting the specific demands of a particular group of knowledge users in terms of analysis, content, presentation, and ease-of-use. Users of a data mart can expect to have data presented in terms that are familiar3. Three-tier architecture A three-tier architecture introduces a server (agent) between the client and the server. Roles of the agent are many, it can provide translation services (adapting a legacy application on a mainframe to a client/ server environment), metering services (acting as a transaction monitor to limit the number of simultaneous request to a given server), or an intelligent agent service (mapping a request to a number of different servers, collating the results, and returning a single response to the client) see example 1. Another example would be the accounting software Platinum for Windows. This software optimizes the balance of processing between the client workstations, file server, and one or more application servers. Tasks, such as pos...