An XML representation of data defined by ISO/TS 14048:2002 has been obtained using the Web Ontology Language (OWL).
The ontology is contained in two files:
The 'Box' example data is represented using these ontologies in file box_example_level_0.owl.
The representation of the data defined by annex A of ISO/TS 14048:2002 is a document structure which specifies the text items to be recorded for a process and for an input or output flow. OWL provides documentation for the XML tags used to represent this data.
At this level, the information is represented by just three classes of object:
The processes and flows are described by properties which have text string values.
The level 0 representation has a property for 'aggregation type' that has a text string as a value. A more formal approach would recognise that a concept such as 'horizontally aggregated' is a class defined within ISO 14048. This class has a name in English, but could also be given a name in other languages.
The use of OWL provides a mechanism for the publication of libraries of standard classes on the web. The following ontologies derived from ISO 14048 have been created:
Where ISO 14048 provides examples, rather than an exclusive set, the ontologies can be extended by the user.
There are two other areas in which a web based ontology can be used:
the definition of process classes;
The NACE process classification could be published on the web as an ontology. An example showing just the process class used for the 'Box' example is in nace.owl.
the definition of substances
In the level 0 approach to LCA data, there is a property 'substance name', which has a text string as a value. A more formal approach would recognise that a substance is a class that can have a large amount of information recorded about it - many different names, chemical composition, many different properties.
There are already many substance ontologies on the web using notations such as ChemML. An ontology for the substances used in the 'Box' example is in boxExampleSubstances.owl.
The 'Box' example data is represented using these additional ontologies in file box_example_level_0.1.owl.
2.3.1 Properties and units
It is possible to increase the formality of representation beyond level 0.1. ISO 15926-2 has defined a formal approach to:
Further semantic precision in the representation of LCA data would be achieved by the use of ontologies for these concepts.
2.3.2 Sources and destinations
The concepts of process and flow are dealt with in detail by ISO 15926-2 (these concepts are important to the process industry, and so a process industry information standard is concerned with them).
An increase in formality and semantic precision can be achieved by recognising that:
The relationships between processes and flow can be defined using generic concepts defined within ISO 15926-2.
In the source data for the 'Box' example, COD (Chemical Oxygen Demand) is treated as if it were a substance that flows. The specified amount is treated as if it were the amount of this substance.
More correctly COD (Chemical Oxygen Demand) is a property of a substance that flows. The specified amount is a property of the amount of substance that flows. This distinction is made in the OWL files.