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Loose-Schema Databases and Heterogenous Data
- 3. Task-list management for HP webOS
- 8. losing data is unacceptable
- 10. schema must be updated before data with new source schema can be stored
- 11. storage may be inefficient
- 12. works fine for music meta-data, works poorly for medical tests
- 15. May still enforce field constraints
- 16. Can't enforce foreign-key relations (no JOINs)
- 18. RESTful HTTP API + client libs
- 19. crash-only file is always consistent
- 21. Resolution similar to Subversion: client merge, re-submit
- 23. 1st query against a view is slow; later only require incremental updating
- 24. map func (JS or Erlang) maps document to N-dimensional array of buckets
- 25. reduce func (optional) computes sums, averages, unions, etc over one or more dimensions
- 26. Data From Two Task Systems
- 27. Map-Reduce Completed Tasks Map: for each ancestor path, write [# completed, 1] Reduce: sum 1 st and 2 nd member of pair
- 30. Questions?
Editor's Notes
- range of BP values not same as range of blood glucose, systolic must be greater than diastolic
- Designed to store and report on large amounts of “semi-structured” data “shared-nothing" clustering written in Erlang for robust concurrent systems; no shared state threading and all data is immutable no fixed schema, no declarative schema, update function can check consistency and permissions incremental replication, partial replicas possible; also runs on handhelds
- Simple map func. Can extract subset of documents map+reduce can collect related documents (e.g. blog post & comments)
- Your company uses a traditional Project Planning system, which works in terms of man-hours Blue system has project with two subprojects Your group uses an online task-tracking system like Basecamp Yellow system has three tasks, one of which has a subtask There is also software associated with the CouchDB database, which allows you to specify that yellow tasks are components of blue subprojects From this, we assign a path to each item.
- Goal: Calculate # completed tasks for each item [left] documents in CouchDB (blanks are not null, but fields not present) Map function written in JavaScript, emits 0 or more values, to ANY bin (key) [go through map function for each record]