webMethods Flow is a graphical programming language that runs within the webMethods Integration Server. It was designed to simplify tedious, difficult to maintain or error prone aspects of integration/B2B activities. The Software AG Designer is the IDE in which to write flow code.
History
developed flow as a technology to increase the ease and speed of development on their B2B/enterprise integration platform. A language that would be a suitable fit with the desire for a service-based application server was another driving force.
Philosophy
The main driver behind flow syntax was to allow the graphical configuration of the mapping logic that forms the major part of Integration projects. Transformation and conversion of data in a text basedprogramming language quickly becomes unwieldy and cluttered. It is also quite difficult to maintain due to the cumbersome nature. Flow code seeks to alleviate this problem by creating a programming language similar to the way you would indicate mapping of data if your source and destination data formats were placed side by side on a white board and lines connecting source to destination. The other goal of flow was to allow a service based view of the application. Any existing code is a service. Invoking functionality is akin to treating it as a "black box" requiring certain inputs. The results of that operation are then treated as outputs of the "black box". The concept of the "pipeline" is the means by which to pass data to and get results back from invocation of services.
Syntax
There are the following operators in the flow language:
Map
Invoke
Branch
Loop
Repeat
Exit
Sequence
The operators are stored on disk as XML but this is not generally edited directly, rather the IDE is used.
Advantages
Mapping logic is easily performed and fairly natural to understand.
Allows ease of reuse of existing services via a service based view of code
Automatic exposure of all services as Web Services and use of Web Services as "services" to be invoked
Criticisms
Incorrectly used flow can produce some ugly code due to too much in the way of mapping in a single Map operation.
It is a proprietary language and as such there is little support or reference material available outside webMethods and a few isolated user created pages.
Source code is stored as XML, making it rather difficult to use traditional editors, source control and merge tools.
The graphical nature of the language may give the impression that non-technical staff are capable of writing good code in it. A solid technical background in other programming languages is of great advantage in producing good quality flow code.
Fairly heavily mouse driven compared to java/c++/c# etc. and can result in sore mouse arm while first developing in it
Only the webMethods platform has an implementation, so should a shift from that platform be desired a complete re-write of all flow code is required
Code refactorization is only partially supported by the tool and had to be done by hand
Due to specific approach of viewing and editing the Flow code, in complex implementation is very hard to find and understand existing code, because enforcing multiple mouse clicking at subsequent steps in Flow code to see parameters/details.
