Customization with Standardization: The Architectural Challenge for Corporate GIS applications
Application servers
Application servers distributed architecture ensure delivery of information from one
application to the next and also provides at the server side the ability to process
information from many different resources, such as databases and applications.
Application server is a consistent and reliable programming model mainly because
they require that complex applications be divided into transactions. Application
servers control transactions from their beginning to their end, from the client to the
resource server, and then back again. They ensure ACID (Atomic, Consistency,
Isolation and Durability) properties of transactions. It makes application servers a
natural choice for distributed applications, which must deal with different type of
interfaces and heterogeneous platforms.
Application servers provide a location for the application code to run and, as a
result, a location for business processing and application objects to run, as well as
a location where methods can be shared among applications. They can be used to
enforce business rules and maintain data integrity or to create entire applications
by building many transaction services and invoking them from the client.
They also provide load balancing, thread pooling, object recycling, and the ability to
automatically recover from typical system problems.
Spatial DBMS
In order to have an enterprise GIS solution it is required to have an integrated data
management solution. In the mid-1990s spatial data was tightly integrated with
associated tabular data. This type of solution was not enough to support the
operation requirements of the enterprises. The object-based and object-relational
architecture of the late 1990s provides an open and robust solution to support
these requirements.
The real need was to apply the benefits of mature database management
technology to geographic data. As the evolving growth of users and consequently
transactions, the security and continuous availability requirements and scalability
needs [4] pushed the Database and GIS industry to construct an integrated
solution that is capable of supporting the new business environment.
The way the database industry solved the problem about spatial data was using
the software component technology by introducing components that are stored
inside the database. This feature adds the required types, functions, and other
pieces, making them available at the SQL level. Different applications can take
advantage of different components and as requirements and standards evolve, a
component can generally evolve along with them more quickly than the database
software itself. This solution was possible because of the extensibility of new
object-relational concept of database servers
Some of the benefits that database technology introduced into GIS solutions are:
- Flexibility - SQL provides the flexibility to queries.
- Data integrity – tabular and spatial data stored at the same administrative
policies.
- Scalability – applications are able to support a few to millions of transactions
because of the proven capability of commercial database systems.
- Performance – all available features of commercial database systems like
buffering, B-tree indexes, query execution plan plus the spatial access
methods implementations: Quad-tree, R-tree and Grid.
- Object-relational features – support for creating new and abstract data
types, capability to create any kind of integrity using functions.
- Open standards – SQL and GML access to all functions and operations.
- Support for enterprise applications – the client/server architecture of
database systems is already proved to be the most reliable component of
any EAI solution.
- Heterogeneous data – tools to support heterogeneous geographic data
including projection management and coordinate transformation.
OGC is also involved on Geospatial data access standards. For databases, the
current and most relevant OGC standard is the Simple Features Specification for
SQL [1].
