Connecting iThink and STELLA to a Database
A question we periodically get from our customers is: Can iThink or STELLA connect to a database? Saving and pulling information to/from databases presents a lot of advantages for storing, organizing and sharing model data. Thanks to iThink and STELLA’s ability to import and export data via commonly used spreadsheet file formats, it is possible to use comma separated value (CSV) files as a means to create a connection to database applications.
Essentially, data can be moved between a database and iThink/STELLA by using a CSV file as a bridge. CSV files are a widely supported file standard for storing table data, and both iThink/STELLA and many database programs are able to read and write to them.
The process can be automated when you use iThink/STELLA’s ability to run models automatically from the command line (Windows only). Most database applications also have command line interfaces, allowing you to create a single macro script that moves data between your model and a database in a single process.
In this post I will use a simple example to demonstrate how to import data from a Microsoft SQL Server database into an iThink model on Windows. The model and all files associated with the import process are available by clicking here. If you don’t have access to Microsoft SQL Server, you can download a free developer’s version called SQL Server Express from the Microsoft web site.
The Model
The model used in this example is a variation of the Beer Game model. The structure shown below represents the ordering process for a simple retailer supply chain.
The model has been set up to import the initial values for On Order with Wholesaler and Unfilled Orders stocks, target inventory and actual customer orders (a graphical function with 21 weeks of data). The source of the imported data is the file named import.csv in the example files.
To set up this example, I manually created the CSV file using the initial model parameters. (Later in this post, you’ll see that this file will be automatically created by the database.) The model has been initialized in a steady state with actual customer orders at a constant level of 4 cases per week over the 21 week period.
