The attribute 246093002 | Component (attribute) | which has been used in the Observables model after the disambiguation of the Towards attribute is shared with the Procedure concept model. As the Observables model and the Procedure model have different rules regarding relationship grouping, the Observables PG preferred solution is to create a new attribute separate from the Procedure model attribute. A proposal for naming this attribute is "constituent".
Figure 1. Definition of constituent from Merriam-Webster's dictionary
Note that M-W considers "constituent" and "component" as synonyms. The attribute has the following definition in the Observables I/E document: "For relational property types, e.g. ratios, concentrations, etc., this attributed specifies what is in the numerator of the ratio". The IUPAC Gold Book defines "component" as "Constituent of a mixture the amount or concentration of which can be varied independently". Thus, it seems that the meaning of the two words "component" and "constituent" are very close, at least.
Going through (some) previous non-lab observable examples, this attribute is not used.
Observables PG Meeting 2016-08-01
Rob Hausam: the two are synonyms, without difference in meaning, hence, why shoudl there be different attributes? The reasons are purely technical. Proposal to make two (sub-)attributes Procedure component and Observable component. Cf. Procedure site and Finding site.