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A model for Context-aware Databases

A model for Context-aware Databases. What is Context?. Ο καθένας ορίζει το context διαφορετικά... “location, identities of nearby people and objects, and changes to those objects” “environment or situation” etc… Δύο πιο γενικοί ορισμοί:

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A model for Context-aware Databases

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  1. A model for Context-aware Databases

  2. What is Context? • Ο καθένας ορίζει το context διαφορετικά... • “location, identities of nearby people and objects, and changes to those objects” • “environment or situation” • etc… • Δύο πιο γενικοί ορισμοί: • Contextis any information that can be used to characterize the situation of an entity. • A system is context-aware if it uses context to provide relevant information and/or services to the user, where relevancy depends on the user’s task.

  3. Motivation • Πολλά διαφορετικά μοντέλα για την περιγραφή του context. • Όμως τελικά η διαχείριση της πληροφορίας με βάση το context γίνεται στο επίπεδο των εφαρμογών. • Redundancy: Η λογική και οι βασικές λειτουργίες υλοποιούνται από κάθε εφαρμογή ξεχωριστά. • Οι υλοποιήσεις εξαρτώνται στενά από τη φύση της κάθε εφαρμογής και τις επιλογές κατά τον σχεδιασμό της. • Maintenance overhead.

  4. Motivation • Ο στόχος είναι: • Ομοιόμορφος χειρισμός της πληροφορίας και του context που την χαρακτηρίζει. • Διαχείριση του context ως «first class citizen»από τα ΣΔΒΔ. • Πλεονεκτήματα: • Καλύτερος σχεδιασμός. • High level query language. • Efficient access/optimization. • Μηχανισμός για consistency checking ως προς το context.

  5. Context Definition • World • environment under which data obtain a substance. • Dimension • the set of parameters used to specify the worlds. • example set of dimensions D = {device, payment} • Context specifier • [device=PC] • [device=PDA, payment in {credit card, cash}] • Universal context: [] • Empty context: [-]

  6. Example • Web site about digital cameras. • Information entity dcamera with attributes: • Brand,Model, MPix, Photo, Price • Dimensions: • device ranging over {PC, PDA, CELL} • payment ranging over {Credit Card, Cash} • Photo: defined only for worlds withbrowsing device in {PC,PDA} • Price: defined in every worldbut its values may change

  7. Context Relation dcamera

  8. Context-Project πModel[ ], MPix[ ], Price[ ]dcamera

  9. Context-Project πModel[Device=PC,Payment=CreditCard], MPix[Device=PC,Payment=CreditCard], Price[Device=PDA,Payment in {CreditCard,Cash}]dcamera

  10. World Project κ[w1,w4]dcamera

  11. Entity Context-Select σentity(BRAND[ ]=‘Kodak’AND MPix[]>3)dcamera

  12. Entity Context-Select σentity(BRAND[ ]=‘Kodak’AND MPix[]>3)dcamera σentity(Price[Device=PC,Payment=Cash] < Price[Device=PC,Payment=CreditCard])dcamera σentity(BRAND[ ] = Kodak AND Price < 250)dcamera Πως αποτιμάται το condition στους κόσμους όπου δεν ορίζεται ένα attribute?? NO context specifier  evaluate the condition to true if there existsat least one world where the condition holds.

  13. Facet Context-Select σfacet(Price < 500)dcamera

  14. Context Relation accessories

  15. Context Cartesian Project/Join

  16. Illustrating Example • Ctx-Rel1context cartesian product(dcamera, accessories) • Ctx-Rel2σentity(dc.Model[ ] = ac.Model[ ] AND BRAND[ ]=‘Kodak’AND dc.Price[Device=PC,Payment=Cash]<400)Ctx-Rel1 • Result πdc.Model[Device=PC,Payment=Cash], dc.Price[Device=PC,Payment=Cash], ac.Name[Device=PC,Payment=CreditCard],Ac.Price[Device=PC,Payment=CreditCard]Ctx-Rel2

  17. CR vs Relational model • Relational implementation: • A single demoralized relation. • Number of different worlds relations. • The link between the facets of the same entity is lost. • The link between the same attribute under different worlds is lost.

  18. Future Work • Extend the relational calculus and algebra to incorporate context. • Context-aware query language for the CR model. • Possible uses of CRModel • Time/histories of data. • Personalization/profiles. • Web/mobile services. • Design efficient access methods to take context into account. • Query optimization.

  19. Ερωτήσεις ?????? ???? ?????

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