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Sun, 2005-Jan-09

TransactionSafe turns 0.4

After more than four months of very occasional half-hearted hacking TransactionSafe has reached version 0.4. This version is titled "Basic Register" or alternatively "I was too embarrassed to release yet another version which still didn't support basic transaction entry!".

This version includes a few interesting design points, although they may be obscured by a fairly rushed and stream-of-conciousness flow of python programming. As with previous versions I've based the user Load/Save paradigm around a commit-as-soon-as-you-can model. There is no save button because the file is always saved. Pity there is no undo. Well, that can come later ;)

Another feature is my attempt to use "processes" sort-of-modelled after the Erlang message passing system. Essentially, each object gets told when to execute by an evalaute scheduler. At that time their input is already there (as it has been passsed on by another process) and ready to be processed into output. I think I've been able to achieve a reasonable amount of decoupling between components using this model, although it is still highly-experimental (meaning non-obvious and hard to read).

Third on my list of novelties is the way the program interacts with the sqlite database. The database itself (with some transformations applied) is considered the model in my MVC, and I have walked a path of updating everything using the same inefficient simple algorithm rather than custom-coding update features. You can see this in the diference between the account tree (which is based on the micro-update model) and the register (which is the newer code based on a single update mechanism). The round-trip to the database occurs often (every time a single field is updated), and I even went so far as to use the python difflib to determine which parts of the gtk tree model that makes up my register to update. That is to say, the gtk tree model likes to be updated minimally so that the user is still in the same place they were in the tree before the update. I've taken the raw tree model from disk each time, and passed it through a diff algorithm filter to determine what that minimal update is without the need for custom code for inferring.

This version makes use of triggers for database updates, particularly to maintain certain database invariants such as "all transactions balance". I've waited this long to do it because for a long time I wasn't sure exactly how I was going to enforce that constraint. Now I maintain a Balance account that must always exist as transactionEntryId 0, and is referred to in every transaction at least once (multiple currencies each get their own balance entry). This meshes with the current user interface/database interaction paradigm nicely.

Now that the triggers are in place, it should be possible for other applications to touch the database without too much risk of trashing the underlying conceptual model. This is core to my intentions for this work and is a step up from the gnucash line of a closed file format under a open (but subject-to-change) C api deep inside the gnucash codebase.

This version is still based on a "core" financial data model. As yet it doesn't even include a default currency for accounts, let alone account types that might direct the register to call the Debit and Credit columsn something friendlier. I'm hoping that I'll get around to designing and demonstrating the use of multiple rdf schemas in the same SQL database at some point to allow expansion for various application needs (share price download could use another schema integrated into the same database, for example).

In the end this version is significant because it represents my second motivation point in the development of this software. My current list is:

  1. Actually contribute some open source software, instead of just bitching (complete, v0.1)
  2. Try not to be completely full of hot air by getting transaction entry working (complete, v0.4)
  3. Make this program a usable alternative to Quicken for my own finances (todo)
  4. Establish a small user-base (todo)
  5. Establish a developer community (todo)
  6. Profit! (todo. damn.)

Hopefully the energy required to overcome these peaks of resistence will not be too great :) At present I'm still just a little pissant who can't manage to play with any of the big boys and who has therefore unreasonbly set out on his own. The best I could hope for at present is to fracture an already anemic developer and user home and small business financial software community. <sigh/>