David Winter posted a comment, noting that he had been unable to find the ISO securities data model in the ISO Web site (that's financial securities – stocks/shares/etc.). The reason that it isn't there is that ISO 19312 is still a work in progress, it hasn't yet been approved (indeed, it hasn't yet started reached the ISO voting stage yet). As such, it isn't yet generally available, although you may find that you can get a copy of the current draft of the data model from your local ISO/standards representatives if you are involved in banking and finance.
David is currently looking at MDDL, which is the best place to be looking in the meantime. Indeed, ISO 19312 will only cover a subset (more or less) of what MDDL covers, at least initially. David seems a little perturbed or surprised that MDDL puts trading terminology (snap, time-series) at the top of its document hierarchy, but in my experience most surprises that people have about standards are usually due to people assuming different requirements to those that were used (or otherwise disagreeing with the requirements that were used). MDDL, for example, was originally designed for distributing financial market data (from stock exchanges and such), so it's not surprising that it talks about snaps (snapshots) and time-series, which are what people look at when they look at market data. MDDL isn't just a financial instrument data model, as ISO 19312 is (but note that ISO 19312 also covers corporate actions – changes to the details of securities because companies have merged, split, changed name, or because of other similar reasons). David considers MDDL to be inverted, so I guess the way he would have done the requirements would have been inverted, in some sense, as compared to the way they were done (and there's often no good or bad in these things, just choices that have to be made, one way or the other).
For anyone who is looking at MDDL as a data model, note that the most versions of MDDL have their data model defined in an XML file (e.g. “mddl-2.5-beta.xml”), which is a simple XML format constrained by a Schema (e.g “mddl-2.5-beta-schema.xsd”). The latest version of MDDL, 3.0-beta, comes with the data model in the form of a UML model (and documentation generated from that model is supplied with the release).
If you feel you must reverse-engineer a data model from the MDDL Schema, please use the “lite” or “base” version of the Schema, as the full Schema implements a number of MDDL-specific “ shorthand” structures which don't make sense if directly reverse-engineered as a data model.