Various Workflow Questions

Question

I'm new to workflow and I'm trying to figure out the best way to construct my app.
First, what is the best method of generating the item key?
Second, when creating a new process how are the attribute values set? CreateProcess doesn't have any method of doing this. Would I need to use SetItemAttr? How would it react if the item didn't yet exist (as createProcess would not have been called)?
Third, what is the best practice for storing data? One could conceivably store the data in tables of their own and not use the attributes at all. They could also store it in both their own tables and the attributes (which seems redundant to me). They could also just use the attributes for storing data (as the examples in the Workflow guide seem to do).
If I only store the data in the attributes, how would I go about presenting it to my users on various web pages?
Perhaps the solution is to store the data in an initial table, load it into attributes during the first function, only access it in the attributes until a final decision is made, at which point the last function would take the data in the attributes and store it in the final table?
Thanks,
Tom

Answer 1

1) Usually the item key is derived from the primary key of the application object being handled by the workflow. For example, in a requisition workflow, a good item key would be the requisition number. The item key does not have to be meaningful, though; from a workflow point of view the main point is that the item key and item type combination must be unique.
2) Yes, SetItemAttr is the right way to set item attributes, and you're correct that CreateProcess must be called first. The best order in which to call the APIs is:
CreateProcess
SetItemUserKey
SetItemOwner
SetItemAttr...
StartProcess
CreateProcess and StartProcess are required; the Set... APIs are optional, if you want to set any of those values. If you do not need to set anything, you can call LaunchProcess instead, which combines CreateProcess and StartProcess in one wrapper; but note that LaunchProcess does not give you any opportunity to set any values in between creating and starting the process.
3) Item attributes are basically meant to hold the information that the workflow process itself needs to use. There is a trade-off between the convenience of storing global process data in item type attributes and the overhead incurred by loading item type attributes when a process instance is created. So we recommend that you do not use item type attributes as a denormalized data store. Instead, always refer back to the base application to retrieve up-to-date values. Minimizing the number of item type attributes will improve the performance of your workflow process. Also, runtime workflow information is usually purged from the WF tables at some time after the process is complete, so any information that you want to access from your own application should be stored back in your own tables.
We recommend that the following types of information should be defined as item type attributes:
- Information required by notification messages, such as the display format of a currency value
- Information required by function activities, such as values that link back to applications data like a person_ID
- Information maintained by a workflow activity, such as data for activities that identify who to forward information to and from in a loop construct
- Business event messages required by Send or Receive event activities, or event details required by Raise event activities