Some of you older folks may remember a time when grocery stores put price stickers on everything. Each can of green beans or salad dressing had a white or orange sticker on it with a price. No barcode, just a simple number like “$1.29″. When you checked out, there was a cashier who could (brace yourself) actually type numbers into a cash register. In fact, she could typically type them very fast with one hand and move the groceries to the bagging area with the other.
One day I noticed that some things that I bought at the grocery store had a new “built in” tag with a lot of lines on it. It seemed completely useless to me because the only thing on it besides the row of lines was a seemingly random series of numbers. I eventually learned that these were called “UPC” or Universal Product Code tags. Since the tags were implemented long before most grocery stores received and installed the cash registers that could read these tags, they seemed rather pointless to most people.
But soon all of that changed. Because each product carried a unique code, and that code was the same for that product whether it was on a store shelf in Akron Ohio or Pascagoula, Mississippi, products could be paid for, inventoried, and ordered all using the UPC number. In fact, those processes eventually became completely automated. Modern checkouts at large chain stores such as Wal-Mart or Target read the UPC code, look up the price, subtract a single item of the matching type from inventory, and if the supply is getting low, automatically order new stock. There are currently some experimental stores that constantly monitor supply and demand and adjust the price of each item in the store based on these real-time statistics!
It is difficult to overstate the far reaching impact the simple UPC has had on the retail industry. It has enabled stores with millions of items in stock to instantly know how many of each item is on the shelf, how many are on order, and how many were sold in the past hour.
That is all very interesting, but what has it go to do with what we are talking about? I am about to tell you!
Before the days of UPC, the task of pricing, inventorying, and ordering stock was very time consuming. Since the cashier only had the price that was paid for an item to enter (not what the item was), there was no way to know how much the inventory of a particular item had been depleted other than manually counting items or, more commonly, “eyeball ordering”. A department manager ordered new stock when the stock on the shelf looked low.
In many ways, the problems they faced had a lot in common with the problems we now face on software projects. We have a huge number of individual pieces which must be assembled in just the right way to work. To make things worse, they are always changing. It would be as if there were gremlins in the store that constantly rearranged the shelves when nobody was looking and mixed different items up. Actually, I think those really did exist. They were called kids. I know because I mixed up a few shelves myself. With this overwhelming amount of information to track and with many, many items changing all the time, something is needed to get the kind of control on project pieces in a similar way UPC codes allowed stores to get control of inventory. We need a UPC for our project pieces.
Enter the Integrity Control Item. This is a concept that treats anything that is versioned (i.e. everything we care about) as a unique item. Similar to the way a can of Green Giant whole kernel corn has a code that is unique throughout the food supply system, our ICI is unique throughout our project. Actually, properly implemented it is globally unique even between projects, but more on that later. For now it is sufficient to say that a ICI is unique in a given project. In our examples, I will just use a numeric value like “324398675″ to represent an ICI.
So what does that do for us? Great. Now instead of worrying about the Oracle Client drivers, I can worry about keeping up ICI #324398675 and its thirty eight thousand brothers. Yea, buddy…that sure made my life easier! But wait…there’s more!
If the only thing we got out of an ICI was a hard to remember number it would be no better than a cell phone, but that is not the case. When a grocery store orders something with a UPC code, when the order comes in, it has additional information with the UPC code.
For example, it may have the manufacturer, the product name, the quantity, and the country of origin. You don’t need to know the country of origin to order the corn, you just need to know the UPC code, but if you need to know what that UPC represents, a large amount of information about it is available in the inventory control system. Similarly, if we want to automatically check that an ICI is present in a particular release, we don’t need to know what it is or what its characteristics are ahead of time, those can be looked up when they are needed or not looked up when they are not. There are many, many other advantages to tracking everything in your project with an ICI which will become more obvious as we dig deeper into this process, but for now I will let you ponder these ideas and try to shoot holes in them.
Next time I will discuss how versioning works with an ICI. I hope you come back to read about it.
-M@
