Product data management (PDM) is the process behind automatically managing all the design data contained in engineering shop drawings.
Back in the day, It was the collective bills of material on a set of shop drawings that were the primary source of all the procurement information. That Bill of material often got turned into spreadsheets so that the data could be entered into a companies purchasing system. The parts and assemblies were numbered and the data entered into the companies production information system
One of the drawbacks to this, is that a lot of information was not always captured by the bill of material. The paint colour, the material finish, special instructions for fasteners were often contained only in notes on the drawing and this information had to be tediously copied one at a time into a companies production information system.
Sometimes there were no actual shop drawings at all. Every bit of information about making a particular product was spread across varied spreadsheets, word documents and handwritten paper sheets in 3 ring binders. In some cases it was all contained in the head of one key employee who had been around long enough to learn every conceivable detail about the products manufacture.
Product data management is the system that tries to replace that single key employee, and all the documents as well with a single source of data entry that takes products from creation to shipping to after sales support.
The first step in unified product data management is to keep every bit of product information in a single place or database. There should be only one location for the product description, part number ,SKU number and so on.
Every department, shipping, engineering, sales through administration refers back to this single database for whatever product information they need
Built into this single database is change management and revision control. When a part or a process gets changed for any reason each revised part is treated as seperate and distinct and complete history is recorded to keep track of what versions were used and with which customers.
This kind of information is essential if you are going to be supplying spare parts and have to know if there are compatibility issues that may arise from shippping the customer a Revision 4 part when he or she may have originally purchased Revision 1.
The PLM system database records dates and times for purchases and for manufactured items which makes it possible to forecast requirements based of previous years demand.