Page 253 - DCAP603_DATAWARE_HOUSING_AND_DATAMINING

Unit 13: Metadata and Data Warehouse Quality

There is no need for you to directly modify the physical store for the Data Warehouse. If you need notes
to extend the Data Warehouse, for example, to encompass third-party data, a site developer can
programmatically add the fields you need through the logical schema.

Logical Schema

The logical schema provides an understandable view of the data in the Data Warehouse, and
supports an efficient import process. For example, a site developer uses the logical schema to
modify the location of data stored in the underlying physical tables. When a site developer writes
code to add, update, or delete data in the Data Warehouse, the developer interacts with the
logical schema. When Commerce Server accesses data in the Data Warehouse, it accesses the
data through the logical schema. Only the site developer needs detailed knowledge of the logical
schema.
A logical schema includes the following:
1. Class: A logical collection of data members. For example, the RegisteredUser class contains
data members describing a registered user.
2. Data member: A structure that stores a piece of data. For example, the E-mail data member
of the RegisteredUser class stores the e-mail address for a registered user.

3. Relation: A connection between two classes in a parent-child relationship. This relationship
defines the number of instances of each class, and it provides the mechanism for sharing
data members between classes. For example, RegisteredUser is a parent to the child class
Request. There can be many requests for one registered user.
The logical schema uses classes, data members, relations, and other data structures to map data
in the physical store.

13.1.2 importing Data to the Data Warehouse

The data that populates the Data Warehouse typically comes from multiple data sources: Web
server logs, Commerce Server databases, and other data sources that you specify. The following
figure shows the sources for operational data, and how the data might be used to support tasks
run from Business Desk.

Because the Data Warehouse is not part of your run-time environment, a system administrator
must determine how frequently to import the operational data into the Data Warehouse. For
example, you can set up the Data Warehouse so that it automatically imports new data every day
or every week. The frequency with which you will need to import data depends on the amount
of new data collected every day in your operational data sources. Commerce Server includes
custom Data Transformation Service (DTS) tasks that simplify the importing of data into the Data
Warehouse. These DTS tasks import data that is used with the reports available from Business
Desk.
Even though the operational data can be imported from different types of databases or from
storage media that are not databases—all of the data is structured in a consistent manner after it
is gathered into the Data Warehouse. For example, you might have one data source in which the
first and last name of a user are stored in the same field, and another in which the first and last
names are stored in separate fields. When this data is imported into the Data Warehouse, it is
automatically structured to be consistent, thus enabling your analysis activities.

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