This is the final part of an eight-part series describing how to design a database for a Workflow Engine. Check out Part 1 here:
We've now completed the database design for our Workflow Engine, so let's take a look at the final database diagram (click here for a larger view):
That's a lot of tables! But we're trying to design a generic engine, one that can be used for many disparate processes, and as such the complexity of this design reflects the complexity of the requirements.
Shortcomings of This Design
There are a few shortcomings of this design:
- Currently, there's no way to say "Stay in this state for X days; after X days, move to another state." We cannot cause Requests to move along in the Process due to time elapsed.
- We don't have a procedure in place to handle a State or Transition ceasing to exist (meaning, even though the Process Admins are supposed to be able to change the Process itself, what happens when they actually do that?)
- The RequestFiles table stores the actual files in the table itself; a more performant way to do this would be to store the files on a filestore somewhere and just keep references to them in this table.
- We don't currently have a way to designate that a specific individual needs to perform an Action or receive an Activity.
That said, most of these shortcomings are fairly easy to implement; we actually did solve a few of them for our company's workflow engine.
Remember: this is only a database schema. The design doesn't account for how this service would actually be implemented in code.
Whew! That was a lot of steps! But what we ended up with was a generic, extensible, reusable workflow engine database design that can handle a huge variety of processes.
Thanks for reading! If you found this series helpful (or just need to yell at me for something I did incorrectly) let me know in the comments.