Architecture model . One crucial issue that has been discussed is the
definition of a highly modular three-tier architecture where the middle-tier
acts as a software glue between the relational database and the object-
oriented data structures of the suite of local editing and remote browsing
Distribution paradigm . An accurate analysis has been conducted in order
to identify the distribution paradigm best suited to support the remote
visualization of cartographic maps in a web browser. The alternative choices
were the declarative paradigm of Java Servlets and the mobile code para-
digm of Java Applets. The latter was chosen because it better supports
graphical user interactivity.
Middleware technology . Multiple disparate technologies combine in the
development of an internet-based geographic information system: data
storage in a relational database, data transmission using sockets and data
visualization through Java Applets.
Data exchange format
Distributed systems integrate applications and resources
that are heterogeneous and not able to interoperate.
They are usually implemented using different
technologies, different languages and for different
While indeed any application can pass any data to any
other application, each distributed application has its own
semantics which define the specific usage constraints on
shared data, the specific transformations that can occur
and the relationship of those transformations to particular
types of messages.
Forces or tradeoffs
In the past, EDI technology has been proposed as a
mechanism to allow heterogeneous applications to
exchange multi-format documents. Its limit is the
excessive rigidity of the standard format. In the opposite
direction, a different solution consists of managing
multiple and evolving classifications of terms and
concepts structured in specialization generalization
The extensible mark-up language (XML) is a uniform data
exchange format among distributed applications. XML
documents are semi-structured, as they have a flexible
syntactic structure based on tag (mark up) nesting, which
may contain unstructured information. Following the
original spirit of the W3C recommendation (www.w3c.org)
that introduced XML, a generic XML processor should be
able to process a generic XML document.