Asset Topology as a Graph: Why Industrial Hierarchies Lose Information

#Abstract

Industrial asset registers are modelled as hierarchies because the standards that govern them describe hierarchies. Physical plants are not hierarchical, and forcing the topology into a tree either duplicates nodes or misrepresents connectivity. This report characterises the mismatch, proposes retaining the standard hierarchy as one edge type within a multi-relational graph, and reports what changes in query behaviour.

#The mismatch

Standards for enterprise and control system integration define an equipment hierarchy of enterprise, site, area, work centre and work unit [1]. This is genuinely useful: it gives a shared vocabulary and a boundary between operational and enterprise systems.

Three common physical arrangements violate the tree:

1. Shared headers. A distribution header serves units in several areas. Under a tree it belongs to one area and its relationship to the others is unrepresentable.
2. Site utilities. Instrument air, cooling water and power cross the entire site. Their correct parent is the site, and their functional relationships are with equipment several levels down.
3. Shared spares and swing equipment. A unit that can be lined up to either of two trains belongs to both, and to neither exclusively.

The two available responses under a tree are duplication, which breaks identity, and arbitrary assignment, which makes the structure lie about connectivity. Both are observed in operating asset registers.

#Construction

The proposal is to represent topology as a labelled multi-relational graph in which the standard hierarchy is one edge type among several rather than the structure of the data [3].

1contains        the ISA-95 hierarchy, retained and queryable as before
2feeds           process connectivity, from the drawings
3measured_by     instrumentation attached to equipment
4isolates        valves and their isolation relationships
5spare_for       swing and shared equipment
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The hierarchy remains fully available: a query for everything under an area is a traversal restricted to contains edges. What changes is that connectivity questions no longer have to be answered through the hierarchy, which is what forced the distortions.

#Why the information model matters more than the values

Interoperability protocols for industrial equipment carry an address space with typed nodes, references between them and attached semantics [2]. A client that reads only values discards the type information and the reference structure, then reconstructs both by hand, per site, from documentation.

Importing the information model rather than the tag list is therefore the practical route to a populated graph. The mapping is performed once per site by type instead of once per point.

#Ranking and explanation

Once topology is a graph, the operational question becomes what is related to a given asset, which requires ranking. A hop-decayed product of edge confidence and type weight, optionally augmented with a centrality term [7] and structural link prediction over shared neighbours [8], is sufficient in practice.

The finding worth reporting is that ranking quality was not the limiting factor on adoption. A ranked list without a stated reason was not used by operators. Rendering the shortest path as a sentence, using one phrase per edge type, changed the feature from ignored to used, and no amount of weight tuning produced a comparable effect.

#Security constraint

Populating the graph requires data from control systems, which are protected deliberately. An architecture in which the monitoring path is one way by construction rather than by policy [6] is what makes the deployment acceptable to the organisation responsible for the control system, and it constrains the design from the beginning rather than at review.

#Limitations

No user study supports the explanation finding. It rests on observed usage before and after the change on a small number of sites, with no controlled comparison, and it is the claim in this report most in need of proper evaluation.

The edge type vocabulary above is drawn from process industry practice [4] [5] and is not proposed as a standard. Whether a common vocabulary across industries is achievable is not addressed.