A process specification perspective on Life Cycle Assessment

Towards a formal ontology for describing LCA methodology

Introduction

Life Cycle Assessment (LCA) is a methodology for studying a product system, from a sustainable engineering viewpoint, and quantifying and evaluating the environmental burden of that product system during its entire lifecycle. By objectively understanding the environmental profile of a product system, it becomes possible to propose and evaluate alternative product systems with potentially lesser environmental impact, where the results of the study are used to drive decision making. LCA considerations are highly important and should be factored into any product design engineering programme right from the start of the design process. There is an International Standard for LCA, which is set in ISO14040:2006 and available as a textual document.

LCA in the context of process specification

LCA, in essence, is comprised of a set of well-understood kinds of activities that need to be appropriately planned in order to reap maximum benefit from the study. For example, the methodology consists of the goal and scope definition, followed by inventory analysis, followed by impact assessment, and finalizes with life cycle interpretation. Altogether these areas provide a perspective on the kinds of methodology activities. During the course of LCA study, consideration needs to be given to things that are the participants in the methodology and influence it, e.g., people, deliverables required at various stages, topics that need to be documented, etc. These concepts provide a perspective on the objects that define how the activities are to be planned and resourced. Furthermore, if we consider the actual execution of LCA methodology, i.e., actually carrying it out in real-time, then this implies that we need to consider the occurrence of LCA activities and how they span over time. This requires a perspective on the occurrence and temporal aspects in LCA execution.

With this in mind, we can say that LCA methodology description and execution falls neatly within the scope of activities, objects, activity occurrences and timepoints. This means that there is potential to develop an ontology of LCA following a suitable process specification framework, primarily because process specification provides coverage for that scope. One such coverage is supported by the Process Specification Language (PSL) ontology, which is itself an International Standard ISO18629–1:2004. In this post, we’ll highlight how LCA could be placed in the context of the PSL ontology and we’ll also discuss what could be done in order to leverage and extend PSL for LCA methodology description capture (in fact, the points we’ll highlight here can be applied to any methodology description that uses the basis of process specification).

Activity

In PSL, an activity is regarded as a reusable behaviour, e.g., the activity of writing a blog post, which can have several occurrences (because we can publish unique blog posts about specific topics, at specific times) or may not occur at all (e.g., if we choose not to write a blog post). We can say that the various stages of LCA methodology are kinds of activities, whose instances are activities that associate with specific product systems. Hierarchies of activity types can be defined for the stages of the LCA methodology. This high-level activity perspective on LCA methodology stages provides ways of capturing methodology and generic programme management description.

Activity occurrence and timepoint

In PSL, an activity occurrence is a unique occurrence of an activity, with specific start and end times. Note that a distinction is required between activity occurrences and activity instances. This is because, an activity instance is a reusable behaviour that may or may not occur at all. An activity occurrence, on the other hand, is bound to happen and spans over time. The activity occurrence and temporal perspective supports the definition of the project planning and execution side of LCA practice.

Object

In PSL, objects are those things that are neither activities, nor activity occurrences, nor timepoints. Objects are concrete or abstract entities that can participate in and influence activities and their occurrences. In LCA, things like people, governmental and non-governmental organisations, product functions, flow diagrams, metrics, documented reports, deliverables, etc., are all objects.

Using PSL to define LCA

The diagram shown at the top of this post exemplifies, in a simple way, how we can start using PSL to capture LCA methodology description and execution semantics. The example uses some of the very basic intuitions from PSL. The PSL concepts of Activity and Object are good for organising the notions that are necessary for the description of LCA methodology. Hierarchies of activity types are, however, necessary in order to provide the classification structures for the kinds of activities that constitute LCA methodology. Similarly, hierarchies of object types are needed to reflect the range of object intuitions present in LCA.

On the other hand, the PSL concepts of Activity Occurrence, Timepoint and Object can be used for the description of LCA methodology execution semantics. Process execution semantics is where the PSL ontology is particularly strong, with several formal theories specifying relations, axioms, definitions, etc. In the example shown here, a couple of very basic relations are shown across one object, an activity occurrence and its start and end timepoints.

Discussions and conclusions

The primary strength of PSL lies in the area of activity execution semantics meaning that it targets predominantly real-time process representation. For this reason, PSL can support modelling LCA project planning and execution. However, since a big part of what makes up LCA is related to describing how the methodology works, this implies that additional work is required in the area of activities and objects, in order to accommodate methodology description semantics. There are several obvious areas where extensions to PSL would be necessary, e.g., by defining relations that describe participation, behaviour, influence and other associations specifically holding for objects and activities.

References

• ISO14040:2006. Environmental management — Life cycle assessment — Principles and framework.
• ISO18629–1:2004. Industrial automation systems and integration — Process specification language — Part 1: Overview and basic principles.