Interoperability meeting S. Derriere, Strasbourg, 2003 October 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 ???

Interoperability meeting S. Derriere, Strasbourg, 2003 October 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

Interoperability meeting S. Derriere, Strasbourg, 2003 October 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 M km/s UCD here

Interoperability meeting S. Derriere, Strasbourg, 2003 October 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

Interoperability meeting S. Derriere, Strasbourg, 2003 October 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

Interoperability meeting S. Derriere, Strasbourg, 2003 October 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

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

Interoperability meeting S. Derriere, Strasbourg, 2003 October 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,...

Interoperability meeting S. Derriere, Strasbourg, 2003 October 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

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

Interoperability meeting S. Derriere, Strasbourg, 2003 October 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)