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Trio: A System for Data, Uncertainty, and Lineage
Search “stanford trio”http://i.stanford.edu/trio
2
People
Current• Jennifer Widom (faculty)• Omar Benjelloun (post-doc)• Parag Agrawal, Anish Das Sarma, Shubha Nabar (PhD)• Michi Mutsuzaki (MS)• Tomoe Sugihara (visitor)
Incoming• Martin Theobald (post-doc)• Raghu Murthy (MS)• Ander de Keijzer (visitor)
Alums• Alon Halevy, Ashok Chandra (visitors)• Chris Hayworth (MS)
3
Why Uncertainty + Lineage?
Many applications seem to need both
From a technical standpoint, it turns out that
lineage...1. Enables simple and consistent
representation of uncertain data
2. Correlates uncertainty in query results with uncertainty in the input data
3. Can make computation over uncertain data more efficient
4
Trio Components
1. Data Model ULDBs (Uncertainty-Lineage Databases): Simple extension to relational model
2. Query Language TriQL: Simple extension to SQL, well-defined
semantics and intuitive behavior
3. System Version 1: Complete system and GUI built
on top of conventional DBMS
5
Running Example: Crime-Solving
Saw(witness,car) // may be uncertain
Drives(person,car) // may be uncertain
Suspects(person) = πperson(Saw ⋈ Drives)
6
Our Model for Uncertainty
1. Alternatives
2. ‘?’ (Maybe) Annotations
3. Confidences
7
Our Model for Uncertainty
1. Alternatives: uncertainty about value
2. ‘?’ (Maybe) Annotations
3. Confidences
Saw (witness,car)
(Amy, Honda) ∥ (Amy, Toyota) ∥ (Amy, Mazda)
witness car
Amy { Honda, Toyota, Mazda }
=
Three possibleinstances
8
Six possibleinstances
Our Model for Uncertainty
1. Alternatives
2. ‘?’ (Maybe): uncertainty about presence
3. Confidences
Saw (witness,car)
(Amy, Honda) ∥ (Amy, Toyota) ∥ (Amy, Mazda)
(Betty, Acura)?
9
Our Model for Uncertainty
1. Alternatives
2. ‘?’ (Maybe) Annotations
3. Confidences: weighted uncertainty
Saw (witness,car)
(Amy, Honda): 0.5 ∥ (Amy,Toyota): 0.3 ∥ (Amy, Mazda): 0.2
(Betty, Acura): 0.6?
Six possible instances, each with a probability
10
Models for Uncertainty
• Our model (so far) is not especially new
• We spent some time exploring the space of models for uncertainty [ICDE 06, journal]
• Tension between understandability and expressiveness– Our model is understandable
– But it is not complete, or even closed under common operations
11
Our Model is Not Closed
Saw (witness,car)
(Cathy, Honda) ∥ (Cathy, Mazda)
Drives (person,car)
(Jimmy, Toyota) ∥ (Jimmy, Mazda)
(Billy, Honda) ∥ (Frank, Honda)
(Hank, Honda)
Suspects
Jimmy
Billy ∥ Frank
Hank
Suspects = πperson(Saw ⋈ Drives)
???
Does not correctlycapture possibleinstances in theresult
CANNOT
12
Lineage to the Rescue
Lineage• Captures “where data came from”
• In Trio: A function λ from alternatives to other alternatives (or external sources)
13
Example with Lineage
ID Saw (witness,car)
11
(Cathy, Honda) ∥ (Cathy, Mazda)
ID Drives (person,car)
21
(Jimmy, Toyota) ∥ (Jimmy, Mazda)
22
(Billy, Honda) ∥ (Frank, Honda)
23
(Hank, Honda)
ID Suspects
31
Jimmy
32
Billy ∥ Frank
33
Hank
???
Suspects = πperson(Saw ⋈ Drives) λ(31) = (11,2),(21,2)
λ(32,1) = (11,1),(22,1); λ(32,2) = (11,1),(22,2)
λ(33) = (11,1), 23
Correctly captures possible instances inthe result
14
Uncertainty-Lineage Databases (ULDBs)
1. Alternatives
2. ‘?’ (Maybe) Annotations
3. Confidences
4. Lineage
ULDBs are closed and complete[VLDB 06]
15
ULDBs: Lineage
• Conjunctive lineage sufficient for most operations
• Duplicate-elimination: Disjunctive lineage
• Difference: Negative lineage
• General case after multiple operations/queries: Boolean formula
16
ULDBs: Interesting Questions
• Data-minimality: extraneous alternatives, extraneous “?”
• Lineage-minimality: harder
• Membership: tuple and table, some-instance and all-instances
• Coexistence: multiple tuples
• Extraction: remove tables, retain possible-instances
17
Example: Extraneous Data
(Diane, Mazda) ∥ (Diane, Acura)
Dianeextraneous
(Diane, Mazda)
(Diane, Acura)
?
??
18
Example: Coexistence
Mazda
Acura
(Diane, Mazda) ∥ (Diane, Acura)
(Diane, Mazda)
(Diane, Acura)
?
??
?Can’t coexist
19
Querying ULDBs: Semantics
Query Q on ULDB D
DD
D1, D2, …, DnD1, D2, …, Dn
possibleinstances
Q on eachinstance
representationof instances
Q(D1), Q(D2), …, Q(Dn)Q(D1), Q(D2), …, Q(Dn)
D’D’implementation of Q
operational semanticsD + ResultD + Result
20
Querying ULDBs: TriQL
Basic TriQL: SQL with new semantics• Obeys commutative diagram for uncertain data
• Tracks lineage
• Query results: new table or on-the-fly
Implemented TriQL: also built-in predicates conf(), lineage(), lineage*()
21
Additional TriQL Constructs
[Language manual on web site]
• “Horizontal subqueries”Refer to tuple alternatives as a relation
• Unmerged (horizontal duplicates)
• Flatten, GroupAlts
• NoLineage, NoConf, NoMaybe
• Query-specified confidences [done]
• Data modification statements
22
Confidence Computation
• Confidences computed on-demand based on lineage—Confidence of alternative A is function of
confidences in λ*(A)
—Permits any query plan for data computation
• Default probabilistic interpretation, but queries can override
SELECT person, min(conf(Saw),conf(Drives)) as confFROM Saw, DrivesWHERE Saw.car = Drives.car
23
Trio System: Version 1
Standard relational DBMS
Trio API and translator(Python)
Trio API and translator(Python)
Command-lineclient
Command-lineclient
TrioMetadat
a
TrioExplorer(GUI client)
TrioExplorer(GUI client)
Trio Stored
Procedures
EncodedData
TablesLineageTables
Standard SQL• “Verticalize”• Shared IDs for alternatives• Columns for confidence,“?”• One per result table• Uses unique IDs
• Table types• Schema-level lineage structure
• conf()• lineage() “==>”• lineage*() “==>>”
• DDL commands• TriQL queries• Schema browsing• Table browsing• Explore lineage• On-demand confidence computation
24
Current & Future Topics
Algorithms: confidence computation, coexistence
extraneous data• Minimize lineage traversal• Memoization• Batch operations
System• Full query language• More internal processing ?
– Storage and indexing– Statistics and query optimization
25
Current & Future Topics
• Top-K by confidence
• Extend basic uncertainty model—Incomplete relations
—Continuous uncertainty
—Correlated uncertainty ?
• External lineage, update lineage, versioning