Home > SSW Standards > Developer .Net > SSW Application Design Architecture Supporting Web Services
This document outlines the design architecture of SSW's software development
projects. We use a multi-tiered approach which can support the use of web
services if need be - allowing our applications to have complete support for
access from locations outside of our network.
Figure: Diagram of SSW Application Design - Adam's Version
Figure: Diagram of SSW Application Design - Ross' Version
Frontend Windows
The front-end contains only the GUI and basic interface related code. A
couple of examples of what the front-end filename could be are:
- SSWTimePRO.exe (recommended)
- Northwind.exe
Our front-ends are always written in Microsoft Visual Basic.NET. Our
reasoning for this is that:
- It is a friendlier language for less experienced developers (i.e.
interface designers, etc) to be working with.
- It has declarative events (via the Handles statement)
- We prefer our developers to have active experience with both C# and
VB.NET - thus, we implement both in our projects (our business layer is
written in C#, as described below)
The following concepts and rules are used in our development of this
tier:
How This Layer Communicates
- This layer talks to the Middle Tier (or Business Objects) as in logic and
partitioning, obviously not physically as all assemblies live on the same PC
- the functionality is exposed via a reference to Business.dll.
Example of a standard data entry form
|
Form Name |
Purpose |
frmCustomer
(Inherits from frmBase - has standard style definitions and
functionality such as action buttons, etc) |
Data Entry form |
|
frmCustomerSearch |
Form that lists records that match a user's
search criteria |
|
frmCustomerList |
Lists all records of a particular type |
One to Many display strategy
- Always show the many as subforms i.e. as pages on the tab control in VB.NET
(ie. frmCustomerOrderSub, frmCustomerContactSub)
- Populated with data only as needed, but since a rich client can have state, do not lose the data until move to a new customer record
Figure: Related data displayed in a sub-form
Frontend - Web
This area is also written in Microsoft Visual Basic.NET (our reasons for
doing this are described in the above section)
Frontend - ASP.NET
|
Form Name |
Purpose |
|
Customer.aspx |
Data Entry form |
|
CustomerList.aspx |
Lists all records of a particular type |
One to Many display strategy
- Always show the many as subforms ie. as pages on the tab control in ASP.NET
(ie. frmCustomerOrderSub, frmCustomerContactSub)
- Populated with data only as needed, but since a web client shouldn't have state, do not attempt to keep the data ie. show one subform at a time
Business Objects
Examples of Names:
- Business (recommended)
- NorthwindClassLibrary
- MiddleTier
Coding
The Middle Tier (or Business Objects) is essentially ADO.NET code written in
C# talking to stored procedures - no direct actions (INSERT, UPDATE, DELETE) in
inline SQL
- Customer.Select(strWhere, strCnn)
- Use a DataSet as it is a static snapshot of data, suitable for
transport across a web service (DataReaders aren't)
- Customer.Insert(..., strCnn) - Use sqlCommand DC
- Customer.Update(..., strCustomerID, intConcurrency, strCnn)
- Use sqlCommand DC
- Customer.Delete(strCustomerID, intConcurrency, strCnn)
- Use sqlCommand DC
Backend
The backend is our data store - it's typically running on SQL Server or MSDE.
Examples of Names:
- SSWTimePRO2000 (recommended)
- Northwind
Coding
Stored procs are better but they are more expensive for the customer. Therefore this is the suggested compromise.
Stored procs for action for data integrity.
SQL OK for SELECT
Web Connectivity/Web Services
The web services layer provides access to our business service via SOAP (an
XML-based object access protocol that runs over HTTP).
Examples of Names:
- WebServices (recommended)
- NorthwindWebService
This is then implemented by creating a virtual directory in IIS that points
to a collection of ASP.NET web service files, which in turn serves as a pointer
to the Business Objects class.
Coding
In order to provide this access, we need to make our Middle Tier
web enabled. This is done by adding [WebMethod] attributes to all functions.
Security is a consideration that should be taken seriously - after all,
having this layer present will provide a publicly accessible gateway to all data
in your backend!