----- Original Message ----- From: "Greg Woodhouse" <gregory.woodho...@sbcglobal.net> To: <hardhats-members at lists.sourceforge.net> Sent: 2006-04-10 10:46 AM Subject: Re: [Hardhats-members] Software Archetypes - single vs double systems
> What I find most frustrating about discussion of archetypes is that it > is so often vague and intuitive in nature, making it rather hard to > decipher. > > --- Bill Walton <bill.walton at charter.net> wrote: > > > Software Archetypes - single vs double systemsHi Lorie, > > > > Archetypes provide a capability that's very familiar to programmers, > > but take it to the next level. At the most basic level, it's about > > decoupling. An RDBMS shields programs from the need to know about > > the underlying structure of the data. A program needs only know > > about the db schema. Views provide another level of abstraction, > > shielding programs from changes in the schema. Archetypes (which I > > believe do not depend on an RDBMS implementation) provide a similar > > capability, but take it to the domain level. > > By domain do you mean application domain? Or are you referring to > domains in their technical sense in database theory (as a set of > values)? At any rate, it is clear that you are trying to abstract away > from a particular set of units, treating the quantity itself as a value > (not how it might be represented). > > > > > When working with an archetype-enabled system, programs / programmers > > work directly with domain concepts like blood pressure or height or > > weight. The underlying data is stored / accessed through the > > archetype. > > But what does this mean? It suggests that an archetype is realizable as > a computational object (much as a schema may be realized as a set of > relations, or a class instantiated to form an object). I suspect that > this is the point at which an important concept is missing: The > integers are a ring, but when I add two numbers, I'm not using the + > operation of the category Ring, but rather of a specific member of that > category, namely Z. > > > A trivial example of the benefits would be lbs. vs. kgs.. > > In an archetype-enabled system, the program has no knowledge of the > > unit-of-weight measure used to store the data. Programs access the > > data store with statements like (no representation made re: syntax) > > store_weight(220, lbs) and patient_weight = > > retrieve_weight(patient_id, kgs). > > Okay, here is some concrete syntax, but what are you really doing? Is > kgs a flag or map (or something else altogether)? From a mathematical > point of view, it's natural to think of it as a scaling transformation > (a map). But that's confusing, too, because it implies the existence > of some reference instance out there (say kilograms) that is somehow > privileged among other possible choices, and that your kgs flag is > simply the scaling factor (isomorphism) you need to apply to get your > chosen representation. > > > > You might want to take a look at > > http://oceaninformatics.biz/archetypes/MindMap/ArchetypeMap.html for > > a better, high-level understanding of the above. This, and a good > > deal of the related stuff, will be migrated shortly to the openEHR > > site. > > > > Be happy to provide / get you more in-depth info if desired. > > > > hth, > > > > > === > Gregory Woodhouse <gregory.woodhouse at sbcglobal.net> > > "It is foolish to answer a question that > you do not understand." > --G. Polya ("How to Solve It") > > > ------------------------------------------------------- > This SF.Net email is sponsored by xPML, a groundbreaking scripting language > that extends applications into web and mobile media. Attend the live webcast > and join the prime developer group breaking into this new coding territory! > http://sel.as-us.falkag.net/sel?cmd=lnk&kid=110944&bid=241720&dat=121642 > _______________________________________________ > Hardhats-members mailing list > Hardhats-members at lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/hardhats-members
