The design of Analysis-Operators in GIS covers structure and behavior. Behavior has
to be defined
as the abstract function performed by the operator, independent of data structure.
Structure describes the way an operator is designed to perform data structure independent
processing. An operator is able to analyze input data, to select an adequate operation depending
upon the kind of input data, and to return output data. Inside the operator, data driven selection
processes ensure that adequate algorithms are chosen to analyze the specific input data types.
To understand what happens inside an operator, the view of a multi-shell object just
like an onion
comes into one's mind, symbolizing to a certain degree a hierarchical structure. In case of
universal operators, we see three different levels:
The management level is the outmost shell the user interacts with. At
this level, a certain problem
of an information community is tackled through the knowledge and experience of the user. The
medium for the problem solution is offered in form of the above GUI with visual programming
capabilities and universal operators. Users can use stored graphs, create new graphs, change and
assign parameters to the operators and create their personalized solutions. Communication takes
place through the use of metadata in data catalogues and the operators. Metadata are passed
through the chain of activated operators.
Semantic of an operator is realized at the control level (mid level)
where input data, metadata and
the supplied parameters are analyzed and translated into the adequate processing chain
Processing then is performed on a very low level (processing level),
depending upon the distributed
computing platform, operating system, and the software environment.
Management (High Level):
At high level, the semantics of the operation is defined. The data to be analyzed
are selected from
the data catalogue with their associated metadata. The operator is specified upon its
parametrization which is also metadata driven. This level manages the whole operator. It is the
constituent part of the analysis task. The user defines the operation upon his cognitive experience.
The data description at this level is independent of any spatial data structure (e.g.
raster or vector)
or data schema.
Controlling (Mid Level):
At mid level, the controlling of the operation is carried out. The input data, selected
at high level,
are linked to their corresponding data representations in a geometric and structural level. The
operator analyzes the metadata, given at the management level, and chooses the algorithm that
matches the data types and other requirements. Here, the requirements for hybrid analysis
functionality arise because of the different data representations.
At this level, the cognitive semantics of the data and operation gets lost, the information
translated into syntactically structured information for the processing in which their cognitive
context is unimportant.
Processing (Low Level):
The low level is the processing level. The algorithm processes the data numerically,
characteristics are processed and sent back to mid level.
A universal analytical GIS-operator is characterized by its functionality. It is important
to look upon
this functionality in the context of input and output data (see Figure
The universal operator is able to analyze the input data to choose the appropriate
processing. As a result, new output data are generated. A High-Level-Operator therefore has to be
metadata driven. For selecting data and functionality, only metadata will be used. The following
survey introduces the concept of operators and their input and output data.
Input data are described through
a data catalogue including its metadata and lineage information.
The link to their digital representation in the related and implemented data schema has to be
The operator is defined by
a generic method. This is specified by its characteristic parameters. The
operation is described by the operators metadata. The operator generates specific metadata as a
protocol for the lineage. The underlying control has to select the correct algorithm that fits the
types and structures of the input data. Each algorithm has its own profile. The process control
executes an analysis of the data as an inquiry for the right algorithm. The operator is designed in
polymorph way which includes hybrid operations.
Output data are mapped
into a data catalogue which may already exist. Otherwise a data
catalogue including metadata and lineage information has to be generated. Its representation is
linked to the underlying data schema. The output data catalogue may be derived from the operator,
or the operator has to meet the conditions of the data model chosen by the user.
The functionality of a GIS-Analysis-Operator can be divided in the three categories geometric
converter, semantic translator, and metadata
All geographic data have a geometric
component. One of the main goals of spatial analysis is to
solve geometric (metric and topological) questions. Generally a GIS analysis produces data with
new geometric information. Consequently a GIS- Analysis- Operator converts the geometric input
into the new geometry of the output data.
Semantics of data is assigned by the
Information Community on the basis of a conceptual model
with attributes and descriptions. It is located above the underlying geometry. The geometric
process of the operator is linked to the thematic component of the data, a new theme is generated
during the combination process with the geometric and semantic overlay. The result is a new
The Operator is controlled and prepared for processing, based on the metadata of
the input data.
Metadata is translated to process control parameters. The process produces new metadata. The
generation of the output metadata is controlled by the operations metadata.
The controlling of the operator includes the preconditions that are derived from the
input data and
the chosen operation with its implemented algorithms. For the output, the postconditions include
the requirements of the output data. The operation has to be protocolled including the lineage and
other metadata (Jung and Albrecht 1997).