4 ms·

I don't really see much connection with what OMG have done. Yes, they did do a little work on an Ontology Definition Metamodel, but I wouldn't take that too ser

by larsga 8y ago

I don't really see much connection with what OMG have done. Yes, they did do a little work on an Ontology Definition Metamodel, but I wouldn't take that too seriously. I don't think they understood what they were doing. Similarly, I don't think graph databases have that much in common with RDF. Yes, both are graphs, but they're quite different, really.

PaulHoule 8y ago
What I've seen with OMG-promulgated standards is that the people involved know what they are doing but (1) they do a bad job communicating it, (2) people do a bad job of understanding it, (3) as with the W3C compromise in the standards process leads the specification to miss the last 20% that you need to make something that really works, and (4) some adopters of the standard see filling that last 20% as what differentiates them from competitors, so the standard is not so standard. There are many homologies between W3C and OMG standards, one of them is that there is a mapping between the semantics of documents and the semantics of API calls, object definitions, etc. linking all the way back to the CORBA standards. Another is between the XSLT/XPath functions and the "Object Constraint Language". The OMG and W3C maintain a largely overlapping list of primitive data types, for instance. Neo4J and similar products tend to support the "property graph" model which can be modeled with RDF/SPARQL. As for document databases, that gets to the magic about RDF which is most obscure: a document full of facts is an RDF "graph". You can take the union of all of the facts in two documents and that is also a graph. You can take the union of all the facts in two million graphs and run SPARQL queries on it without doing any data transformation or import! This is a necessary condition for a "universal solvent" for combining data from multiple sources but RDF standards haven't been sufficient. Serious semwebbers know about techniques like "smushing" that go a long way towards finishing the job, but oddly these are not incorporated into standards or widely known among beginners.
- larsga 8y ago
  These mappings is exactly what I'm talking about. I advised the OMG on one of the mappings in the ODM and I don't think they understood what they were mapping. To model OWL with UML gives you very little. To then map Topic Maps into the same level as OWL is ... just misguided. Semantics means something very different to the OMG from what it does to the RDF/OWL community. That's the root of the problem. To the RDF/OWL folks it means "mathematically based logical inference of new statements", whereas to the OMG it seems to mean "human-readable text". Yes, you can map a property graph into RDF, but to make it work well you usually have to add a lot of information that's not in the original data. Thanks, I know how RDF and SPARQL work.
  - PaulHoule 8y ago
    UML is not the only standard pushed by the OMG. CORBA and related standards have well-defined semantics. So does BPML. Human-readable definitions are important. One thing I see missing in both the OMG and W3C worlds is a realistic approach to model visualization. For instance if you try to draw a large OWL ontology or a large UML diagram you might need to blow it up to a full wall just to see everything, never mind understand it. Really you need to be able to paint on graphical elements to a graph to show what nodes and relationships are relevant to a particular situation or use case. Many people don't understand OWL because it doesn't actually "make sense". That is, without mechanisms for data validation, you don't know that inference is going to proceed in a correct way, rather you get a "garbage in garbage out" situation where you get new bad facts. Given that the official explanation doesn't make sense, it is natural that people fall back on something they understand.

by larsga 8y ago

PaulHoule 8y ago

What I've seen with OMG-promulgated standards is that the people involved know what they are doing but (1) they do a bad job communicating it, (2) people do a bad job of understanding it, (3) as with the W3C compromise in the standards process leads the specification to miss the last 20% that you need to make something that really works, and (4) some adopters of the standard see filling that last 20% as what differentiates them from competitors, so the standard is not so standard. There are many homologies between W3C and OMG standards, one of them is that there is a mapping between the semantics of documents and the semantics of API calls, object definitions, etc. linking all the way back to the CORBA standards. Another is between the XSLT/XPath functions and the "Object Constraint Language". The OMG and W3C maintain a largely overlapping list of primitive data types, for instance. Neo4J and similar products tend to support the "property graph" model which can be modeled with RDF/SPARQL. As for document databases, that gets to the magic about RDF which is most obscure: a document full of facts is an RDF "graph". You can take the union of all of the facts in two documents and that is also a graph. You can take the union of all the facts in two million graphs and run SPARQL queries on it without doing any data transformation or import! This is a necessary condition for a "universal solvent" for combining data from multiple sources but RDF standards haven't been sufficient. Serious semwebbers know about techniques like "smushing" that go a long way towards finishing the job, but oddly these are not incorporated into standards or widely known among beginners.

larsga 8y ago
These mappings is exactly what I'm talking about. I advised the OMG on one of the mappings in the ODM and I don't think they understood what they were mapping. To model OWL with UML gives you very little. To then map Topic Maps into the same level as OWL is ... just misguided. Semantics means something very different to the OMG from what it does to the RDF/OWL community. That's the root of the problem. To the RDF/OWL folks it means "mathematically based logical inference of new statements", whereas to the OMG it seems to mean "human-readable text". Yes, you can map a property graph into RDF, but to make it work well you usually have to add a lot of information that's not in the original data. Thanks, I know how RDF and SPARQL work.
- PaulHoule 8y ago
  UML is not the only standard pushed by the OMG. CORBA and related standards have well-defined semantics. So does BPML. Human-readable definitions are important. One thing I see missing in both the OMG and W3C worlds is a realistic approach to model visualization. For instance if you try to draw a large OWL ontology or a large UML diagram you might need to blow it up to a full wall just to see everything, never mind understand it. Really you need to be able to paint on graphical elements to a graph to show what nodes and relationships are relevant to a particular situation or use case. Many people don't understand OWL because it doesn't actually "make sense". That is, without mechanisms for data validation, you don't know that inference is going to proceed in a correct way, rather you get a "garbage in garbage out" situation where you get new bad facts. Given that the official explanation doesn't make sense, it is natural that people fall back on something they understand.