clarify what negative pattern elements really mean

[hoechp]

Previously, we decided to get rid of those sub-graphs inside of PatternGraph, which already made things a lot easier.

But it's not exactly clear to me, what negative pattern elements mean - at least not in every case.

PatternNodes, PatternEdgess and PatternAttributes have the action attribute, which usually should be "match", "create" or "remove". Additionally they all have the negative attribute, which only makes sense for those with action == "match". So probably, we could get rid of this negative attribute, too - and replace it with another value for the action attribute. It could just have "==", "!=", "+" and "-" as values, for example.

So to get to the point - my interpretation is:

• a negative PatternNode matches exactly those Nodes, the positive PatternNode would not match (concerning only its attributes).
• a negative PatternEdge from one PatternNode to another means, that they can only match Nodes, that don't have this edge between them
• a negative PatternAttribute means the attribute is not allowed to fulfill the condition

[hoechp]

What I got wrong (here's an example): node with attribute 'type': 'Car' and edge to negative node with attributes 'type': 'Wheel' and 'color': 'blue' means "a car that has no blue wheel".

A negative node is not supposed to match with anything. Effectively, you look for a match of the rest of the Pattern - not minding the negative node. Whenever a match is then found, you try to find this negative node in context of the current match. If you don't find it - it's all fine. If you do find it, this match doesn't work out and the search continues with the next valid configuration of matchable nodes for the main pattern. Something like that. Gotta figure that out and write some tests!