Using metadata for standardisation
Because of the challenges described in the previous article, work of the Ghent Workgroup lead to the creation of a new ISO standard (ISO 19593) called Processing Steps. In full the standard is called: "Use of PDF to associate processing steps and content data". Content data here obviously refers to the design elements itself, what will be printed. Processing steps refers to this additional "non-design" information stored in the PDF document.
So how does this standard work?
Use of layers
The PDF standard has a built-in feature called "Optional Content Groups" (OCDs). This is commonly referred to as "layers" though it's important to realise that there are important differences between layers such as you might know them from Adobe Photoshop or Adobe Illustrator and optional content groups. Layers in design application typically reflect stacking order: the objects in the front layer are "on top" of objects in all other layers. This is not the case for optional content groups; PDF documents can contain an optional content group that contains all images in the document, regardless of their stacking order. And moving an element from one optional content group to another, doesn't change it's stacking nor the visual appearance of the document.
These optional content groups are used to gather all elements belonging to a processing step. All vector elements that form the die cut line for example, are placed in an optional content group. Such optional content groups have a name that can be used to easily identify them.
Attaching metadata to layers
Of course using optional content group names to identify them, would bring us right back to the problem of standardisation; everyone would use their own version of a name... To solve this, the processing steps standard uses metadata attached to the layer for the actual idenfication. Each layer has two pieces of identifying metadata attached to it:
Identifies what kind of processing step this is. Possible groups are "Structural", "Dimensions", "Braille", "Legend", "White", "Varnish" and "Positions".
Identifies the type of processing step in that particular group. In the group "Structural", possible types include "Cutting", "Creasing", "Gluing" and so on.
Using spot colors in layers
Using layers and metadata associated to layers, solves the standardisation problem for processing steps information. However, the elements that are in such a layer still need to have a color, and it makes the most sense to continue to use spot colors for this.
Because of the layers though, these spot colors can be named whatever the designer wants them to be named. As long as the proper processing steps metadata is used, they can be identified regardless.