Page 238 - DCAP603_DATAWARE_HOUSING_AND_DATAMINING

Data Warehousing and Data Mining

notes The main difference in our approach resides in the following points:
1. A clear distinction between subjective quality goals requested by stakeholder and objective
quality factors attached to data warehouse objects.
2. Quality goal resolution is based on the evaluation of the composing quality factors, each
corresponding to a given quality question.

3. Quality questions are implemented and executed as quality queries on the semantically
rich metadata repository.
Figure 12.3 shows the DWQ Quality Model. The class “ObjectType” refers to any meta-object
of the DWQframework depicted in the first layer of figure 12.3. A quality goal is an abstract
requirement, defined on an object types, and documented by a purpose and the stakeholder
interested in. A quality goal roughly expresses natural language requirements like “improve the
availability of source s1 until the end of the month in the viewpoint of the DW administrator”.
Quality dimensions (e.g. “availability”) are used to classify quality goals and factors into different
categories. Furthermore, quality dimensions are used as a vocabulary to define quality factors
and goals; yet each stakeholder might have a different vocabulary and different preferences in
the quality dimensions. Moreover, a quality goal is operationally defined by a set of questions to
which quality factor values are provided as possible answers. As a result of the goal evaluation
process, a set of improvements (e.g. design decisions) can be proposed, in order to achieve the
expected quality. A quality factor represents an actual measurement of a quality value, i.e. it
relates quality values to measurable objects. A quality factor is a special property or characteristic
of the related object with respect to a quality dimension. It also represents the expected range of
the quality value, which may be any subset of a quality domain. Dependencies between quality
factors are also stored in the repository. Finally, the method of measurement is attached to the
quality factor through a measuring agent.
figure 12.3: DWQ Quality Meta Model

232 LoveLy professionaL university