Environmental Engineering Reference
In-Depth Information
SEAMLESS Client Technologies
The client-server model is a popular design for large and complex applications, not
only for mainframe systems but also for remote systems that provide services over the
Internet. Think of e-mail clients using mail storage servers or applications running
inside a web browser. Confusingly client is used for software as well as hardware.
In general clients are classified as fat clients, thin clients, or hybrid clients (Table
9.1
).
A fat client (also known as a thick client or rich client) is a client that performs
the bulk of any data processing operations itself, and does not necessarily rely
on the server. A thin client is a minimal sort of client, its functionality being limited
to the presentation layer. Thin clients use the resources of the host computer. A thin
client's job is generally just to graphically display pictures provided by an application
server, which performs the bulk of any required data processing. A hybrid client is
a mixture of the above two client models. Similar to a fat client, it processes locally,
but relies on the server for storage data. These are also known as rich clients and
implement both presentation and application layers. In designing a multi-tier
architecture, there is a decision to be made as to which parts of the task should be
done on the client, and which on the server. This decision can crucially affect
the cost of clients and servers, the robustness and security of the application as a
whole, and the flexibility of the design for later modification, porting and reuse.
The SeamServer server application can be accessed by SEAMLESS clients.
Basically we can consider two types of clients: system-to-system and human-to-system.
A human-to-system client is a graphical user interface that allows using
SeamServer functionalities, e.g. to define a project or to visualize results. An initial
client (SeamGUI) is developed as part of SEAMLESS-IF. SeamGUI is a hybrid
client, it has no local storage but does provide local processing. For example in the
case of its SeamPRES component that retrieves calculation result data from
SeamServer and processes it locally to create visualisations (tables, charts, map,
and so on). A hybrid client currently is mostly referred to as a RIA, software appli-
cations running on the user's computer that rely on a server for core functionality
but also have some own logic for an enhanced user experience.
A system-to-system client is a programming interface that exposes the SeamServer
functionality. In this case, there is no user interaction, rather there are just computers
exchanging information (actually the SeamServer application server provides
services that the second computer is consuming). The chosen SEAMLESS-IF
architecture, using open standards whenever possible, is capable of supporting
system-to-system clients. However, this is not a priority within our work, and we
do not envision deploying such clients during the duration of the project.
Table 9.1
Types of clients
Local storage
Local processing
Fat client
Ye s
Ye s
Hybrid client
No
Ye s
Thin client
No
No
