View Issue Details

IDProjectCategoryView StatusLast Update
000426710000-014: PubSubSpecpublic2018-11-02 10:05
ReporterMariusz Postol Assigned ToMatthias Damm  
PrioritynoneSeveritymajorReproducibilityhave not tried
Status assignedResolutionreopened 
PlatformAnyOSANyOS VersionAny
Summary0004267: Part 14 PubSub Section 5.2.3 DataSetMetaData - doesn't describe the semantics of the DataSet structure.
Description

The specification says:

DataSetMetaData describes the content and semantic of a DataSet.

I am not a native speaker but according to

http://www.dictionary.com/browse/semantic?s=t

Semantic is the adjective, the noun is Semantics.

Semantics: the meaning, or an interpretation of the meaning, of a word, sign, sentence, etc. In this case DataSet, but the DataSet as one whole doesn't have common meaning - it is randomly selected list of unrelated values. The structure description includes overall DataSet attributes (e.g. name and version) and a set of fields with their name and data type.

Semantics in context of OPC UA Information Model is described in details in

https://mpostol.gitbooks.io/object-oriented-internet/content/DataDiscovery/

The DataSetMetaData describes only fields encoding. It is a fundamental difference between what the specification says, and what I proposed many years ago. One of the goals of the object-oriented-internet project is how to make the DataSet semantics-aware.

Unfortunately, it leads to misunderstanding. Recently my student asked me "what PubSub has in common with OPC UA" - the answer is the encoding and only encoding - more detailed discussion you can find at:

https://mpostol.gitbooks.io/object-oriented-internet/content/Networking/SemanticData/README.PubSubMTF.html

TagsNo tags attached.
Commit Version
Fix Due Date

Activities

Matthias Damm

2018-06-05 16:09

developer   ~0009103

Changed semantic to semantics but in general the DataSetMetaData provides more than just the field encoding.
It provides

  • Name
  • Description
  • Properties like Unit or Range

Therefore semantics is right even it does not give the full blown information model.

Mariusz Postol

2018-06-10 12:13

reporter   ~0009133

Last edited: 2018-06-10 12:16

Yes, the DataSetMetaData provides more than just the field encoding, but not semantics that can be useful for M2M communication. Name and Description use native language and if well formatted can provide semantics in selected native language. Unfortunately, this information is hard to be understood by machines. Even if you use Artificial Intelligence the Name and Description meaning can be recovered with the probability << 1. In other words, for writing a column in a newspaper the text provides semantics, but try to use a computer to understand this text.

Can you provide any real scenario how to use meta-data to change how to proceed the data, e.g screen position where the data is displayed?

See for example project that is underway and where we need to solve problems like this:

Networking.HMI available at: https://github.com/mpostol/OPC-UA-OOI/projects

It leads to very serious interoperability problem that MUST BE addressed by the specification.

Mariusz Postol

2018-11-02 10:05

reporter   ~0009514

There is a discussion you may be interested:

https://www.linkedin.com/feed/update/urn:li:activity:6463706039991705600

To clarify; in other words - my understanding is that the DataSet concept is copy/past of the subscription concept born at the very beginning of the OPC life cycle. The difference is that the OPC subscription is created in the context of OPC Client/Server connection - it makes them tightly coupled components.

My concern is if it can be applied for the publication/subscription scenario that makes components peer and loosely coupled.

Hope it helps.

Issue History

Date Modified Username Field Change
2018-04-30 14:26 Mariusz Postol New Issue
2018-06-05 16:09 Matthias Damm Note Added: 0009103
2018-06-05 16:09 Matthias Damm Status new => resolved
2018-06-05 16:09 Matthias Damm Resolution open => won't fix
2018-06-05 16:09 Matthias Damm Assigned To => Matthias Damm
2018-06-10 12:13 Mariusz Postol Note Added: 0009133
2018-06-10 12:13 Mariusz Postol Status resolved => feedback
2018-06-10 12:13 Mariusz Postol Resolution won't fix => reopened
2018-06-10 12:16 Mariusz Postol Note Edited: 0009133
2018-10-23 15:46 Jim Luth Status feedback => assigned
2018-11-02 10:05 Mariusz Postol Note Added: 0009514