Surrogate Keys in a Data Warehouse (Web hosting solutions) Surrogate keys,
Surrogate Keys in a Data Warehouse Surrogate keys, as you already know, are replacement key values. Asurrogate key makes database access more efficient usually. In data warehouse databases, surrogate keys are possibly more important in terms of gluing together different data, even from different databases, perhaps even different database engines. Sometimes different databases could be keyed on different values, or even contain different key values, which in the non-computerized world are actually identical. For example, a customer in a department of a company could be uniquely identified by the customer s name. In a second department, within the same company, the same customer could be identified by the name of a contact or even perhaps the phone number of that customer. Athird department could identify the same customer by a fixed-length character coding system. All three definitions identify exactly the same customer. If this single company is to have meaningful data across all departments, it must identify the three separate formats, all representing the same customer as being the same customer in the data warehouse. Asurrogate key is the perfect solution, using the same surrogate key value for each repetition of the same customer, across all departments. Surrogate key use is prominent in data warehouse database modeling. Referential Integrity in a Data Warehouse Data warehouse data modeling is essentially a form of relational database modeling, albeit a simplistic form. Referential integrity still applies to data warehouse databases; however, even though referential integrity applies, it is not essential to create primary keys, foreign keys, and their inter-table referential links (referential integrity). It is important to understand that a data warehouse database generally has two distinct activities. The first activity is updating with large numbers of records added at once, sometimes also with large numbers of records changed. It is always best to only add or remove data in a data warehouse. Changing existing data warehouse table records can be extremely inefficient simply because of the sheer size of data warehouses. Referential integrity is best implemented and enforced when updating tables. The second activity of a data warehouse is the reading of data. When data is read, referential integrity does not need to be verified because no changes are occurring to records in tables. On the contrary, because referential integrity implies creation of primary and foreign keys, and because the best database model designs make profligate use of primary and foreign key fields in SQL code, leave referential integrity intact for a data warehouse. So, now we know the origin of data warehouses and why they were devised. What is the data warehouse dimensional database model? 174 Chapter 7
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