All the information about the conceptual descriptions and about the according
database objects involved are represented within the M4 model and stored
within relational tables. “M4-Cases” denote a collection of
steps, basically performed sequentially, each of which changes or augments
one or more concepts. Each step is related to exactly one operator, and
holds all of its input arguments.
Compiler
The M4 compiler reads the specifications of steps and starts the
according executable operator, passing all the necessary inputs to it.
Depending on the operator, the database might be altered. In any case
the M4 meta-data will have to be updated by the compiler. A machine learning
tool to replace missing values is an example for operators altering the
database. In contrast, for operators like a join it is sufficient to virtually
add the resulting view – together with corresponding SQL-statement
– to the meta-data.
The task of a case designer, ideally a data mining expert, is to find
sequences of steps resulting in a representation well suited for data
mining. This work is supported by a special tool, the case editor. Usually
a lot of different operators will be involved in a case of preprocessing
steps. A list of available operators and their overall categories, e.g.Feature
Construction, Clustering or Sampling is part of the conceptual case model
M4. In every step the case designer chooses an applicable operator, sets
all the parameters of the operator, assigns the input concepts, input
attributes and/or input relations and gives some specifics about the output.
Applicability conditions are considered in two ways. On one hand, constraints
of operators can be checked on the basis of meta-data. These are, for
instance, the presence or absence of NULL values. On the other hand, the
conditions of operators can be checked on the basis of the business data
when running the case. Applicability constraints and conditions support
the case designer by checking the validity of a sequence of steps while
it is created.
The sequence of many steps, namely a case, transforms the original database
into another representation. Each step and their ordering is formalized
within M4, so the system is automatically keeping track of the performed
activities. This enables the user to interactively edit and replay the
case or parts of it. Further more, as soon as an efficient chain of preprocessing
has been found, it can easily be exported by just submitting the conceptual
meta-data.
