Chapter 3. Designing the Target Structure

We have our entire source structures defined in the Warehouse Builder. But before we can do anything with them, we need to design what our target data warehouse structure is going to look like. When we have that figured out, we can start mapping data from the source to the target. So, let's design our target structure. First, we're going to take a look at some design topics related to a data warehouse that are different from what we would use if we were designing a regular relational database. We'll then discuss what our design will look like, and after that we'll be ready to move right into creating that design using the Warehouse Builder in the next chapter.

Data warehouse design

When it comes to the design of a data warehouse, there is basically one option that makes the most sense for how we will structure our database and that is the dimensional model. This is a way of looking at the data from a business perspective that makes the data simple, understandable, and easy to query for the business end user. It doesn't require a database administrator to be able to retrieve data from it.

When looking at the source databases in the last chapter, we saw a normalized method of modelling a database. A normalized model removes redundancies in data by storing information in discrete tables, and then referencing those tables when needed. This has an advantage for a transactional system because information needs to be entered at only one place in the database, without duplicating any information already entered. For example, in the ACME Toys and Gizmos transactional database, each time a transaction is recorded for the sale of an item at a register, a...

Data warehouse design in OWB

The Warehouse Builder contains a number of objects, which we can use in designing our data warehouse, that are either relational or dimensional. OWB currently supports designing a target schema only in an Oracle database, and so we will find the objects all under the Oracle node in the Project Explorer. Let's launch Design Center now and have a look at it. But before we can see any objects, we have to have an Oracle module defined to contain the objects. If you've been following along and working through the examples in this book, so far you should have one module already defined for the ACME web site orders database—ACME_WS_ORDERS. We created this in the last chapter when we imported our metadata from that source. If that is the case, our Project Explorer window will look similar to the following:

Creating a target user and module

We need a different module to create our target objects in. So before going any further, let's create a new module in the Project Explorer...

Summary

We have now gone through the process of designing the target structure for our data warehouse. We began with a very high-level overview of data warehouse design topics, then talked about dimensional design and the relational versus multidimensional implementation, and then we discussed the differences between them. As was mentioned earlier, there are other books that are devoted solely to this topic and it would be good to read one or more of them to learn more about design than we've been able to cover here. Our design for ACME Toys and Gizmos is very rudimentary, just to give us an introduction to designing in OWB. You'll want to read in more detail about design when you tackle a real-world design because you may run into other issues we didn't have time or space to cover here.

We're going to take this up now and actually implement the design in OWB in the next chapter.