...but I can just concatenate the various keys together...

That should work, but make sure there is some delimiter between the keys so that you cannot get unintentional overlaps. For instance:

key1  key2  concat concat.
123   45    12345  123.45
12    345   12345  12.345
[download]

Furthermore, you would probably be better off to not expose this key to the outside world, as it contains information about the way your database is structured. You probably want to make an MD5 string out of that so that you have a unique identifier and not expose any information to the outside world.

Liz

The proprietariness of gif has an expiry date. That expiry date has passed for those of us in the USA. It will be over in every country on June 20, 2004. See this timeline. Given the legal climate in Europe, I doubt that the European version was ever enforcible. (IANAL and all that.) Those two between them cover most of Perlmonks.

Therefore the issue of not using .gif for intellectual property reasons is lessening in importance, and all things considered, I would not worry about it too much. (FWIW I am in the USA, where it expired already.)

Excel made it remarkably easy to change from GIF to PNG formats (just changing a parameter). And the image quality is pretty much the same, so that worked well. Thanks!

I like your first approach, since the chart data is coming from a query returning multiple records. If I read what you are suggesting correctly, I don't have to worry about time-stamps at all, just check the hash values. That would allow much longer time-to-refresh values for the files.

Personally I don't think the time-stamp is necessary. But your original post said there was a requirement of not generating a new image within 48 hours. The timestamp is used for that purpose. If your data is pretty static, you can certainly drop that 48 hour checking bit.

If any suggestions are welcome, I suggest ditching Excel. GD::Graph appears to cope with creating the bargraphs (from CB conversation) you're after, but I've not used it.

Ditch Excel? No, I'd shoot Excel slowly and painfully, throw it in a meatgrinder, toss it in between the offensive and defensive lines during a game-ending goal-line stand, slap it a few times, snitch on it to the IRS, soak it in lemon juice, make it listen to modern poetry, THEN throw it in the ditch (either at Love Canal or Times Beach, MO).

That said (and boy do I feel better) I used GD:Graph a while ago and had no problems. If you can use it instead of Excel for this (ie, you have it available or can have it installed quickly enough), I would recommend it.

(And don't get me started on Word's XML ...)

--
tbone1
Rock stars. Is there anything they don't know?
- Homer Simpson

I hate to say it, but I tested GD::Graph and it wasn't as flexible as Excel for charting. For instance, it doesn't allow for error-bars on bar-charts, couldn't mix chart types as easily, required manual calculation of regression lines. Excel's charting is slow, but actually isn't too bad.

• It was quite slow (but we can forgive this)
• It often broke with no apparent reason
• It was unable to cope with moderate-to-heavy concurrency

Please note: I'm not saying you should not automate via Excel, just that it does not seem very fit to me for serving images through a (busy) web server.

About your question, I'd create the file and store it within a table with a key that's related to its information and a timestamp. If - to say - we are talking about stock data, I'd store a key like "XXX-60" to mean it's the stock symbol XXX and the graph is for 60 days. Then I'd store the blob with your GIF and a timestamp. On loading, I'd query the database for a "XXX-60" created within the last five minutes; if not found, I'd create it and replace the old version in the database. I would not go for "real" files; they're harder to keep track of, will fragment the file system, and you need a CGI with a database connection to serve the request in any case.

I mainly went with Excel for convenience: with enough time I'm pretty sure I could get GD to do what I needed (manually add & size error-bars, calculate a regression line, manually overlay graphs to add it, etc.). I guess I'll try adding a simple chart and see how Excel responds.

I like the idea of storing the file in the DB, but won't I need to write that data to disk when I want to display it? If I try to embed it in an HTML page, I'll need a static link for that, will I not?