1. VLDB ‘99 Edinbugh, Scotland Capturing and Querying Multiple Aspects of Semistructured Data Curtis Dyreson (formerly) Dept. of Comp. Sci., James Cook University Michael Böhlen, Christian S. Jensen Nykredit Center for Database Research Department of Computer Science, Aalborg University www.cs.auc.dk/NDB

2. VLDB ‘99 Edinburgh, Scotland2 Outline meta-data representation properties queries collapse match coalesce AUCQL summary

3. VLDB ‘99 Edinburgh, Scotland3 Meta-data database meta-data schema, security, transaction time web meta-data author, language, subject (Dublin Core), privacy web `meta-data’ standards RDF, P3P intrinsic informational, but also exclusional irregular ad-hoc

4. VLDB ‘99 Edinburgh, Scotland4 Movie database movie data Bruce Willis stars in Colour of Night. Colour of Night premiered 1/Jul/1995. publication meta-data language English URL http://www.auc.dk publication date 2/Apr/1997 privacy/security ‘over 18’ publication history v1.2, modified 31/Jul/1998 subject Film, Suspense, Thriller queries Retrieve information published at Danish web sites. Find reviews published in the first week of the movie’s release. Get suspense films starring Bruce Willis.

5. VLDB ‘99 Edinburgh, Scotland5 database edges with labels nodes values A semistructured database &1 Bruce Willis meta-data schema security language URL subject time &2... movie name star age Oscars

6. VLDB ‘99 Edinburgh, Scotland6 Properties property name: property value default name property A label is a set of properties. Colour of Night &1 title Colour of Night &1 name: title Colour of Night &1 name: title URL: www.movie.com

7. VLDB ‘99 Edinburgh, Scotland7 name: title URL: www.movie.com Label semistructure Colour of Night &1 title www.movie.com URL name URLJoe author name meta-meta-data: Joe authored the URL meta-data

8. VLDB ‘99 Edinburgh, Scotland8 Properties (continued) required properties missing properties Colour of Night &2 name: title URL: www.movie.com &1 name: movie security! over 18 required missing the URL property missing the security property

9. VLDB ‘99 Edinburgh, Scotland9 Property semantics transaction time example Color of Night &2 &3 Colour of Night name: title trans. time: [1/Aug/1998 - uc] &1 name: reviewed trans. time: [1/Sep/1999 - uc] name: movie name: title trans. time: [2/Apr/1997 - 31/Jul/1998] &1 &2 &3 Not a path!

10. VLDB ‘99 Edinburgh, Scotland10 Using an existing model meta-data and data edges retrieve titles of reviewed movies SELECT X.data FROM reviewed R, R.movie M, M.title X WHERE R.metadata.transtime INTERSECT M.metadata.transtime AND M.metadata.transtime INTERSECT X.metadata.transtime Colour of Night &1 &2 title 1/Aug/1998 - uc data &3 metadata transtime

11. VLDB ‘99 Edinburgh, Scotland11 Design flaws query must enforce semantics to avoid fictive results SELECT X.data FROM *. title X wildcard unintentionally accesses meta-data no means of enforcing required properties even correctly formed queries are brittle user guesses at meta-data encoding

12. VLDB ‘99 Edinburgh, Scotland12 Outline meta-data representation properties queries collapse match coalesce AUCQL summary

13. VLDB ‘99 Edinburgh, Scotland13 Shortest paths 5 17 3 12 Coalesce min 22 15 22 15 sum Collapse

14. VLDB ‘99 Edinburgh, Scotland14 Collapse Collapse the information along a path to a single edge. Color of Night &1 Colour of Night name: reviewed trans. time: [1/Sep/1999 - uc] &2 &3 name: title trans. time: [2/Apr/1997 - 31/Jul/1998] name: title trans. time: [1/Aug/1998 - uc] name: movie ? ?

15. VLDB ‘99 Edinburgh, Scotland15 Collapse example PropertyCollapse for name is concatenation, for trans. time it is temporal intersection. Color of Night &1 Colour of Night name: reviewed trans. time: [1/Sep/1999 - uc] &2 &3 name: title trans. time: [2/Apr/1997 - 31/Jul/1998] name: title trans. time: [1/Aug/1998 - uc] name: movie name: reviewed.movie.title trans. time: [1/Sep/1999 - uc] name: reviewed.movie.title trans. time: undefined

16. VLDB ‘99 Edinburgh, Scotland16 Match (retrieval) find paths that meet some condition(s) path regular expression role - exact match, e.g., title regular expression operators (.|?*+) (reviewed.movie)*.(title | name) only label matching changes labels are sets of properties required properties values may be from non-string domains, use PropertyMatch

17. VLDB ‘99 Edinburgh, Scotland17 name! movie trans. time: [now - now] LabelMatch example name property - `movie’ compares to `movie’, continue transaction time property - missing in target, continue URL property - missing in query, continue security property - required by database, no match! name: movie security! over 18 URL: www.movie.com query rolelabel in database ? ? ?

18. VLDB ‘99 Edinburgh, Scotland18 Retrieval queries retrieval queries replace only LabelMatch test validity of each path with Collapse cost LabelMatch now O (m) where m is number of properties Collapse is O (m*n) where n is length of path backwards compatible implicit name property LabelMatch is string comparison Collapse can be ignored both kinds of labels can coexist

19. VLDB ‘99 Edinburgh, Scotland19 Additional operations Coalesce - compute a distributed property value &1 &2 name: review security! developer trans. time: [1/Jul/1999 - 15/Jul/1999] name: review security! subscriber trans. time: [16/Jul/1999 - uc] trans. time: [1/Jul/1999 - uc]

20. VLDB ‘99 Edinburgh, Scotland20 Meta-data modification framework is extensible specify the semantics and domain. Or just use it, default semantics. PropertyCollapse PropertyMatch PropertySlice PropertyCoalesce concatenation = semantic error union intersect overlaps intersect coalesce last = semantic error nametrans. timedefault domainstringstime intervalsobjects

21. VLDB ‘99 Edinburgh, Scotland21 Outline meta-data representation properties queries collapse match coalesce AUCQL summary

22. VLDB ‘99 Edinburgh, Scotland22 AUCQL Lorel SELECT statement derivative example, retrieve all movie titles. SELECT Title FROM movie.title Title; AUCQL replaces role with unordered list of properties SELECT Title FROM (name! movie).(name! title) Title; default to required name property

23. VLDB ‘99 Edinburgh, Scotland23 AUCQL (continued) can use any property, retrieve current movie titles SELECT Title FROM (name! movie, trans. time: [now - now]). (name! title, trans.time: [now - now]) Title; can set properties for entire query SET PROPERTY (trans. time: [now - now]); SELECT Title FROM movie.title Title;

24. VLDB ‘99 Edinburgh, Scotland24 AUCQL (continued) can use MATCH, COALESCE, COLLAPSE example, show names along all current paths in the database SELECT PROPERTY(name, COLLAPSE(All)) FROM (trans. time: [now - now])* All; result, e.g, reviewed reviewed.movie reviewed.movie.title …

25. VLDB ‘99 Edinburgh, Scotland25 Summary meta-data representation labels with properties property semantics new query operations extensible AUCQL website implemented research prototype free, downloadable, Unix environment http://www.cs.auc.dk/~curtis/AUCQL interactive query engine tutorials

26. VLDB ‘99 Edinburgh, Scotland26 Related work Lorel (Abiteboul et al., JDL 97) non-simple labels Chlorel/DOEM (Chawathe et al., ICDE ‘98) Deterministic Paths (Buneman et al., ICDT ‘99) RDF query languages (QL ‘98) Query Service for RDF (Decker et al.) P3P (Cranor) RDF Query Specification (Malhotra and Sundaresan)

27. VLDB ‘99 Edinburgh, Scotland27 Future work XML/RDF/DCD translation labels can share common properties no container termination property terminators? recursive semi-structured labels heterogeneous meta-data does security mean security? AUCQL has single property name space dynamic scoping of properties property semantics keyed to single property name

28. VLDB ‘99 Edinburgh, Scotland28 Future work (continued) soundness and completeness incomplete with respect to graph operations minimal set of operations information preserving? property-specific basis design guidelines for property semantics implementation path indexing (when labels have properties) query optimization

29. VLDB ‘99 Edinburgh, Scotland29 Collapse mechanics collapse pair-wise along path LabelCollapse: Label X Label -> Label for each property in both labels if property is in both then apply PropertyCollapse else add to result PropertyCollapse is a property-specific constructor T X T --> T U {undefined} required properties stay required path is valid if no property is undefined