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The Architecture of Gap Inc.'s SCMS PO System

Our Chief Scientist Martin Fowler recently discussed the architecture of GAP Inc.'s  purchase order system, SCMS PO.  Read a snippet below or view the full info deck on martinfowler.com.

SCMS PO is an internal enterprise application. Development began in September 2011 and the application has been in production since December 2011. Interesting design features include using knockout.js form of the Presentation Model pattern, a javascript validator running on both client and server, encapsulating data access with repositories, using MongoDB as an application database, and the testing portfolio.

  • Its purpose is to help Gap Inc. manage purchase orders from suppliers. (SCMS stands for "supply chain management system".)
  • Purchasing staff can put purchase orders (PO) on-screen and make changes depending on the state of the PO.
  • Business logic includes validation of changes and figuring out consequences such as delivery routing and allocation of demands across suppliers.
  • SCMS PO supports a separate service that takes demand orders from upstream forecasting systems and turns them into purchase orders. (An example might be a demand for 100 red T-shirts which SCMS PO might split 60:40 into POs against different suppliers according to its allocation rules.) This demand order service is only an API.
  • There are a few dozen users, scattered around the globe.
  • Much of the talk about web applications centers on dealing with public-facing systems that must handle large volumes of users, but most corporate systems have much lower and constrained loads.
  • On a typical day, 20-30 POs will be updated.
  • On peak days about 200-300 POs will get updates
  • The architecture is designed to handle loads one order of magnitude greater than these.
  • The production code is around 50 KLOC evenly split between Java and Javascript. There is about 75 KLOC of tests, which are a mixture of cucumber, java, javascript, and ruby.

Read the full info deck on martinfowler.com.