Database Reference
In-Depth Information
Employee
places Purchase Order
■
Purchase Orders
are placed with Vendors
■
Purchase Orders
have Purchase Order Details
■
Purchase Orders Details have
Products
■
Products are stored in
Bins
■
Expressed in modeling terms, these relationships look like this:
Employee-1:M-Purchase Orders
■
Vendors-1:M-Purchase Orders
■
Purchase Orders-1:M-Purchase Order Details
■
Products-1:M-Purchase Order Details
■
Bins-1:M-Products
■
Interpreting Legacy Systems
When looking at previous systems, you should have tried to determine not
only the type of data stored (the data model) but also that system's inputs
and outputs. Comparing the data that was stored in the new model is
straightforward. If your customer has kept track of all its products before,
it stands to reason that it will want to do so in the new system. This type of
data can be verified and mapped to the new model. What can be trickier
are the inputs and outputs.
When looking at the previous system, you may find forms or computer
screens that the Mountain View employees or customers were exposed to
during normal business. When you analyze this document, these forms will
offer you critical insight into the types of information that needs to be
stored and to business rules that need to be in place. Take a look at Fig-
ure 6.2, which shows the form that warehouse employees fill out when they
are performing an inventory count.
Looking at this form, we learn a few key pieces of information about
the Product entity. Some of this information agrees with what we found out
earlier from the warehouse manager. First, all products have an SKU num-
ber and a model number. The SKU number is an internal number that
Mountain View uses to keep track of products, and the model number is
unique to the product manufacturer.
Next, we see the format of the BIN Number where products are
stored. When building our model, we now know that the BIN Number
contains both letters and numbers, so we will want to store this data in a
varchar field. Finally, we see again that the products are tracked by serial
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