Randolph, As openEHR has no specification for a persistence model, there is no such thing as a conformant DB schema. At Ocean we have developed a DB schema that is still evolving but this is transparent to any application as the API is based on the openEHR Information Model. We may explore alternate DB schema's and even alternate data store technology, but again this will be transparent to the application.
The main article available on this topic was located at http://www.openehr.org/FAQs/t_persistence_notes.htm but has not yet been moved to the new web site. This is really just some suggestions about how a persistence layer could be implemented, it is by no means a specification for conformance. Regards Heath From: [email protected] [mailto:openehr-technical-bounces at openehr.org] On Behalf Of Randolph Neall Sent: Tuesday, 6 November 2007 2:03 PM To: For openEHR technical discussions Subject: Re: OpenEHR queries Thanks. Of course, as you say, the Sql parser will vary depending on the structure of the underlying store, and underlying store designs can vary, one of the strengths of openEHR. It would still seem, however, that whole chunks of the AQL would have to end up in the Sql, and that, in turn, would have implications--at least some implications--how the underlying store would have to be designed. Only certain schemas would even work with openEHR. Does the openEHR community offer any suggestions? At Ocean you evidently felt that a certain design was best, not just any design, which you imply when you refer to the need to be "conformant." What does it take for a DB schema to be conformant? >The persistence model that Ocean uses is a trade off between completely atomising objects and storing them as blobs. Have you disclosed any of the details regarding this tradeoff? Randolph On 11/5/07, Hugh Leslie <hugh.leslie at oceaninformatics.com > wrote: Hi Randolph, Currently, the only AQL query parser that I know of is one that is part of the Ocean Informatics suite of products and runs against the Ocean EhrBank openEHR repository. Converting AQL to SQL will depend entirely on what your underlying persistence model is and also to some extent what relational database flavour you are using. openEHR doesn't mandate any particular persistence model and as has been already stated, the really nice thing about AQL is that queries are independent of any underlying relational (or object) data model. So an AQL query that is run against two separate and completely independently developed openEHR repositories that probably use a completely separate persistence model should return exactly the same data (as long as they are both conformant). The persistence model that Ocean uses is a trade off between completely atomising objects and storing them as blobs. This has been a process of optimisation and we are really happy with the current performance of the system. This is only one of many possible methods of openEHR persistence. regards Hugh Randolph Neall wrote: I think I understand. Thanks. What actually gets persisted, I suspect, are the paths--and values pointed to by those paths--implicit in your archetype object graph, correct? And to convert AQL query into an SQL query you somehow extract that path from AQL and convert it into some sort of SQL, right? Is there anything on your web site about this, about deriving a DB query from an archtype query? >You can have whatever persistence layer as long as it can get expected results back based on the AQL statement. --That's the question. How do you "get expected results back based on the AQL Statement? Thanks, Randy Neall On 11/5/07, Chunlan Ma <chunlan.ma at oceaninformatics.com > wrote: From: [email protected] [mailto:openehr-technical-bounces at openehr.org] On Behalf Of Randolph Neall Sent: Tuesday, November 06, 2007 3:35 AM To: For openEHR technical discussions Subject: Re: OpenEHR queries As a developer from the US who sometimes tries to follow discussions here, I have a question probably well answered if I took more time myself to find the answer. Against what do your archetype queries run? Against the DB itself or some representation of the data in memory? I ask because a few months ago, someone from openEHR said in one of the discussions that a DB schema is not part of openEHR, that some private participant in openEHR had one for sale, and Ocean, maybe, but that was it. So, again against what do these queries (see example in Chunlan Ma's message below) run? That's good question. You've noticed that I didn't mention anything about the data store here. In general, query languages are designed specifically for a type of data store. For instance, SQL is run against relational databases. XQuery is run against XML structured data. Object Oriented Query Language need to be run against Object oriented database management systems etc. These types of query language are data query languages, i.e. they query at the data level. You have to know DB schema when you write a SQL query statement. Archetype Query Language is different from the general query languages. It's a semantic query language, i.e. it queries data at semantic level. It's neutral to persistence layer and system design. We only need to use archetype path and openEHR reference model to construct AQL statement. You can have whatever persistence layer as long as it can get expected results back based on the AQL statement. That's why AQL queries can be shared across systems and enterprise boundaries. Sharing AQL is one of the key solution to achieve semantic interoperability. Cheers, Chunlan Thanks, Randy Neall Veriqant, L.L.C. On 11/4/07, Chunlan Ma <chunlan.ma at oceaninformatics.com> wrote: Hi Greg, Rong has indicated there is a paper about archetype query language. Thanks Rong. That paper introduced basic query syntax. It was written at the beginning of this year. The query syntax has been enriched recently in order to support more complicated queries. I've already started to write the specifications, but need to resolve some known issues before release. Anyway, I handcrafted the following queries for you (I cannot build my query builder at the moment because of some integration issues). The query statement below shows that all observation instances with respiratory rate greater than n will be returned. SELECT o FROM EHR e[ehr_id/value=$ehrId] CONTAINS COMPOSITION CONTAINS OBSERVATION o[openEHR-EHR-OBSERVATION.respiration.v1.adl] WHERE o/data/events[at0002]/data[at0003]/items[at0004]/value/magnitude>n AND o/data/events[at0002]/data[at0003]/items[at0004]/value/units = '/min' If you want the respiratory quantity object been returned, the query would look like: SELECT o/data/events[at0002]/data[at0003]/items[at0004]/value FROM EHR e[ehr_id/value=$ehrId] CONTAINS COMPOSITION CONTAINS OBSERVATION o[openEHR-EHR-OBSERVATION.respiration.v1.adl] WHERE o/data/events[at0002]/data[at0003]/items[at0004]/value/magnitude>n AND o/data/events[at0002]/data[at0003]/items[at0004]/value/units = '/min' Just for your information, the single letter 'o' is the observation class variable name, "/data/events[at0002]/data[at0003]/items[at0004]/value" is the archetype path to respiratory quantity node. If you have the archetype workbench running, you can identify this path there. '$ehrId' is the parameter name which can be substituted with real EHR ehr_id value at run time. The query language supports parameterization. Some archetype query statements would be very long if the query criteria are complicated. In fact, we don't need to write the above queries by hand. Ocean Informatics has implemented a tool - Archetype Query Builder, which can be used to create/edit queries easily. Additionally, Ocean has also implemented a query parser and query engine as well. The above query statements are consistent to the query syntax introduced by the MedInfo paper. The current query tools also support this query syntax. However, as I have said that we have enriched the query syntax and all the enhancements can be found from the query specifications. Hope this helps. Regards, Chunlan -----Original Message----- From: [email protected] [mailto: <mailto:openehr-technical-bounces at openehr.org> openehr-technical-bounces at openehr.org] On Behalf Of Greg Caulton Sent: Monday, November 05, 2007 6:48 AM To: openEHR-technical at openehr.org Subject: OpenEHR queries Hi, Somewhere I recall reading that there was an OpenEHR query that theoretically an OpenEHR compliant system could execute a return results for. Is there a spec somewhere, preferably with a simple example. So if someone knew my patient and queried for all instances of Respiratory Rate greater than n? openEHR-EHR-OBSERVATION.respiration.v1.adl Rate at0004 > n Units /min (is that a default or are the units passed in the query) Or is this future functionality? thanks Greg http://www.patientos.org <http://www.patientos.org/> _______________________________________________ openEHR-technical mailing list openEHR-technical at openehr.org http://lists.chime.ucl.ac.uk/mailman/listinfo/openehr-technical _______________________________________________ openEHR-technical mailing list openEHR-technical at openehr.org http://lists.chime.ucl.ac.uk/mailman/listinfo/openehr-technical _______________________________________________ openEHR-technical mailing list openEHR-technical at openehr.org http://lists.chime.ucl.ac.uk/mailman/listinfo/openehr-technical _____ _______________________________________________ openEHR-technical mailing list openEHR-technical at openehr.org http://lists.chime.ucl.ac.uk/mailman/listinfo/openehr-technical __________ NOD32 2639 (20071105) Information __________ This message was checked by NOD32 antivirus system. http://www.eset.com <http://www.eset.com/> -- ________________________________________________ Dr Hugh Leslie MBBS, Dip. Obs. RACOG, FRACGP, FACHI Clinical Director Ocean Informatics Pty Ltd M: +61 404 033 767 E: hugh.leslie at oceaninformatics.com W: www.oceaninformatics.com <http://www.oceaninformatics.com/> _______________________________________________ openEHR-technical mailing list openEHR-technical at openehr.org http://lists.chime.ucl.ac.uk/mailman/listinfo/openehr-technical -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.openehr.org/mailman/private/openehr-technical_lists.openehr.org/attachments/20071106/29f37eb9/attachment.html>
