Assembling Cloud-Based Geographic Information Systems: A Pragmatic Approach Using Off-the-Shelf Components - Cloud Computing with e-Science Applications - page 147

Web Server/Hosted Service : This is a web server in the Cloud with
all necessary APIs installed on it. Depending on the cloud service
provider and service provisioning model, this server differs from a
“normal” web server. This cloud web server, ideally, must be hori-
zontally and vertically scalable in the Cloud.
Storage Account : Deploys a cloud-based storage repository that will be
used to store web applications.
Entity Framework Model : This creates a logical view of the database
according to the business logic of the system and gives an abstract view
of the database to the application, hence providing added security.
Web Services : A problem with rich Internet applications is coordinat-
ing the application logic between the middle tier and the presenta-
tion tier. Effective user experience requires the client to be aware
of the application logic that resides on the server. But, it is cumber-
some to develop and maintain the application logic on both the
presentation tier and the middle tier. Our web service solves this
problem by providing services that make the application logic on the
server seamlessly available to the client. That is to say, it allows the
client-side map plug-in to directly interact with the database in an
easy, controlled, and secured way.
Database Server : The geospatial relational database of the application
resides on this server. It has to be a powerful machine as most of the
geospatial data manipulation is performed at this level. The actual
DBMS can be Oracle, SQL server, or SQL Azure as all support geo-
spatial databases.
Figure 7.1 also demonstrates that the process begins with the client when
it sends an HTTP request for the application web page to the web server. The
server responds and reads an appropriate web page from the storage, processes
it, and then sends it to the client. Normally, this page will have a map control
embedded in it that displays the base maps directly from Google or Bing.
Moreover, if a user interacts with the web page, for instance, by selecting
a particular area on the map and searching for something within this area,
the map control and the code behind generate a code-based geospatial query
and send it to the web service that deals with database-related requests.
The web service then passes it to the Entity Framework Model, which then
converts the query into an SQL query tailored to the database server, which
then processes it and sends back the results to the Entity Framework Model.
The model finally invokes the web service communication with the client to
display the relevant area on the map.
The key challenge is the spatial data representation between the client, the web
service, and the database. The database can only keep spatial data in geometry
or geography format, which is not directly produced by Google or Bing map