2. Interoperability meeting S. Derriere, Strasbourg, 2003 October 16-17 UCD2... When all you have is a hammer...... every problem looks like a nail. Registry, service description Problems in the VO: Resource discovery Combine heterogeneous data Answer=UCD ???

3. Interoperability meeting S. Derriere, Strasbourg, 2003 October 16-17 UCD2 are motivated by practical needs. It is not an attempt to build an absolute abstract vision of astronomy. UCD should ensure interoperability between VO components: Do you have this quantity? Can I compare this and that? Standardized description of quantities, between: Fuzzyness of natural language Specificity of data models

4. Interoperability meeting S. Derriere, Strasbourg, 2003 October 16-17 Building UCD2 We need something working. Quick. Conciliate 2 different views: Bottom-up: describe what exists (VizieR, FITS headers...) Top-down: global coherence, UCD3 in mind Concept Property Class Instance Idea of a galaxy Velocity M31 120 km/s UCD here

5. Interoperability meeting S. Derriere, Strasbourg, 2003 October 16-17 Building UCD2 In UCD2: the primary word describes a property Major problem: what is a property ? This can depend on the context. This can depend on the use case. phys.velocity phys.velocity,src stat.error,phys.velocity,src

6. Interoperability meeting S. Derriere, Strasbourg, 2003 October 16-17 Use case What is the price of a red apple ? Query expressed in user's terms. Analyse the query: We must find a value for a property: price We have additional constraints: Fruit type must be an apple Color must be red

7. Interoperability meeting S. Derriere, Strasbourg, 2003 October 16-17 Use case What is the price of a red apple ? Query expressed in user's terms. Find resource, and ask query: SELECT item.price FROM resource WHERE item.fruit.type='apple' AND item.color='red' UCD Not UCD

8. Interoperability meeting S. Derriere, Strasbourg, 2003 October 16-17 Now, what do resources look like ? (resource discovery and querying) item.fruit.type='apple' apples

9. Interoperability meeting S. Derriere, Strasbourg, 2003 October 16-17 Description of resource is critical... in VOTable : addition of a value to a (with associated UCD) ing of fields, parameters No UCD for src.star, or src.galaxy, but src.class exists (concept/instances) src.class='star' src.class='galaxy' Need for a normalized vocabulary for objects types (thesaurus more than UCD) star, late-type stars, early-type stars variable stars, binary stars... galaxies, AGN, BL Lac,...

10. Interoperability meeting S. Derriere, Strasbourg, 2003 October 16-17 Need for useable description of parameters in tables. UCD for instances of photometric bandpasses/filters This is not completely satisfying, but we need it to compensate uncomplete descriptions ! Because we don't have the complete information: : Column name= Vmag Unit = mag Related : ID,instr.bandpass= 'V filter' We use: Column name= Vmag Unit = mag UCD= phot.mag;em.opt.V

11. Interoperability meeting S. Derriere, Strasbourg, 2003 October 16-17 UCD Filters, bandpasses UCD Objects types Data Models utype DAL Translation Layer VOQL VOTable Registry

12. Interoperability meeting S. Derriere, Strasbourg, 2003 October 16-17 Complex quantities Complex = resulting from combination of basic properties. Maths +-/*... Is it relevant to describe this with words ? e.g. Color indices: B-V should we define phot.colorIndex.B-V ? (but what about B-K, J-H, V-I,...) or do we allow something like (phot.mag;em.opt.B)- (phot.mag;em.opt.V)