XML & GIS Application Integration
Methodology
The initial step to be undertaken in any application integration project is to model the
flow and use of the information. Integration methodologies range from simple point-to-
point scenarios to more progressive EAI software products that employ .Business Bus.
architectures (See J.C. Lutz EAI Journal, March 2000, pp. 64-73 for more details on EAI
architectures). Within any given architecture there is the actual passage of information
from one application to another. XML provides a platform- and application-independent
means of transferring the data.
Information Modeling
Information modeling is an important part of EAI integration. An information model
gives data meaning through precise definitions that can be easily communicated with
users. Data must be defined in their static and dynamic states. The messages passed
between applications must also be defined. Several methodologies for creating a model,
used either alone or in combination, are outlined in Professional XML (Martin, D., 2000,
pp. 115-117).
- Workflow models . Focuses on the flow of information between units of work.
- Data flow models . Like workflow only more focus on the information than the business process.
- Object Models . Useful as design tool to model the different .players. in a system.
- Use Cases. Models how certain tasks are accomplished within the GIS and external systems and in the workplace.
- Object Interaction Diagrams . Analyzes the interactions and exchange of information between objects.
Data Representation
Once the information model is complete, the data that will be passed between
applications may be represented in terms of XML. This can be accomplished by object
modeling whereby the elements in the XML document represent objects. The elements
or objects could also represent records in a database. In the following example the parent
object is a work order containing GIS objects that have been placed within a highly
simplified design.
Figure 3
In order to keep the electrical model generic, the GIS objects have been abstracted into
device and conductor objects. Agreed-upon attribute values define the type of device or
conductor that is being placed.
The structure of the work order can be specified in a Document Type Definition (DTD)
to facilitate validation by the XML parser, which will be discussed later. Within the
DTD each element is defined along with the permissible child elements and allowable
attributes for each element.
<!- Example DTD for Work Order ->
Figure 4
If an organization has standardized upon XML there may be existing DTD.s that satisfy
the needs of a given application -- or at least provide a good starting point for DTD
design. .During the design phase, a software developer can look at a DTD and know that
as long as the application he [/she] builds will output documents that conform to that
DTD, other applications can process those documents. (Dick, K., 2000). DTD design is
an effort that is best not performed in a vacuum. The work can be very time intensive up
front so collaboration within the enterprise is advised.
In the event that it is necessary to use multiple DTD.s, developers can create XML
documents that implement .Name Spaces.. Name Space syntax provides a mechanism
to reference multiple DTD documents within a single XML document. Special prefix
tags can be placed on the element tags to specify the DTD that should be used to validate
the data within the element. Name Spaces will not be covered in more detail here but
more information can found in Professional XML (Martin, D., et. al., 2000, pp.237-292)
and on the Web at http://www.w3.org/TR/2000/PR-DOM-Level-2-Core-
20000927/core.html .
DTD.s do have shortcomings. The syntax used to define the DTD is not XML syntax
and requires additional learning. It also does not specify data type constraints for the data
contained in the XML document. It may specify that text must be used within a certain
tag but does not constrain the size of the string, for example. Another alternative to DTD
documents that is designed to overcome the DTD shortcomings is XML Schemas.
XML Schemas are not yet an officially recognized part of W3C.s XML standard, but are
promising .Candidates for Recommendation. because they offer more flexibility in XML
design. Some parsers and organizations have already adopted preliminary
implementations of XML Schemas. Schemas are created using XML syntax and also
support the concept of inheritance and strict data typing. Schemas are covered in more
detail in Professional XML (Martin, D., et. al., 2000, pp.237-292) and on the Web at
http://www.w3.org/XML/Schema
