We present Dexter, a browser-based, domain-independent structured-data explorer for users. Dexter enables users to explore data from multiple local and Web-accessible heterogeneous data sources such as files, Web pages, APIs and databases in the form of tables. Dexter’s users can also compute tables from existing ones as well as validate the tables (base or computed) through declarative rules. Dexter enables users to perform ad hoc queries over their tables with higher expressivity than that is supported by the underlying data sources. Dexter evaluates a user’s query on the client side while evaluating sub-queries on remote sources whenever possible. Dexter also allows users to visualize and share tables, and export (e.g., in JSON, plain XML, and RuleML) tables along with their computation rules. Dexter has been tested for a variety of data sets from domains such as government and apparel manufacturing. Dexter is available online at http://dexter.stanford.edu.

1. Rule-based Exploration of
Structured Data in the Browser
Sudhir Agarwal, Abhijeet Mohapatra,
Michael Genesereth and Harold Boley
DEXTERhttp://dexter.stanford.edu

2. Ad hoc exploration of structured data is often
cumbersome and time-consuming using state-of-art tools
Lots of structured data available on the Web
- Limited or no querying support
E.g. http://www.govtrack.us “Which senators are 40 years old?”

3. - Ad hoc compilation from multiple sources: “Which U.S.
Department Heads attended Stanford University”
- Combining private (local) data with publicly accessible
data

4. DEXTER
Browser-based
Explorer
for Structured Data
runs exclusively on the client side
supports ad hoc queries
http://dexter.stanford.edu

5. DEXTER
Data = Tables
* Extraction and integration of web data by end-users [Agarwal ’13]
*
http://dexter.stanford.edu

6. Rules = Dexlog
Extends standard Datalog with negation,
aggregates, and built-ins
Reference: http://dexter.stanford.edu/main/dexlog.html
Sets and tuples as first-class citizens
e.g. {}, {[“a”,“1”],[“b”,“2”]}
DEXTER
http://dexter.stanford.edu

7. Rules = Dexlog
Reference: http://dexter.stanford.edu/main/dexlog.html
Introduces a specialized operator called setof
q(X,S) :- p(X) & setof(Y, r(X,Y), S)
for all X s.t. p(X) evaluates to true,
SX = {Y | r(X,Y)}
DEXTER
http://dexter.stanford.edu

8. DEXTER
Rules = Dexlog
Reference: http://dexter.stanford.edu/main/dexlog.html
Integrity constraints:
2nd arg of p functionally depends on
1st arg of p
illegal :- p(X,Y) & p(X,Z) &
distinct(Y,Z)
http://dexter.stanford.edu

9. DEXTER
Examples
Hospitals registered with Medicare (hospitals.xml)
http://dexter.stanford.edu

10. DEXTER
Examples
Hospitals registered with Medicare
http://dexter.stanford.edu

11. Examples
Hospitals registered with Medicare in California
misc.hospitalsInCA(NAME) :-
misc.hospitals(NAME,ADDR,CITY,"CA",ZIP,COUNTY,PHONE)
DEXTER
http://dexter.stanford.edu

12. DEXTER
Examples
What is the number of hospitals in each state?
http://dexter.stanford.edu

13. EECS Faculty at MIT
Examples
https://www.eecs.mit.edu/people/faculty-advisors
misc.mitFaculty(A,B,C,D,E,F)
DEXTER
http://dexter.stanford.edu

14. Examples
Turing Award Winners
https://en.wikipedia.org/wiki/Turing_Award
misc.turing(YEAR,NAME)
DEXTER
http://dexter.stanford.edu

15. DEXTER
Examples
misc.mitTuring(NAME) :- misc.turing(YEAR,NAME) &
misc.mitFaculty(NAME,B,C,D,E,F)
Faculty at MIT who have won
a Turing Award
http://dexter.stanford.edu

16. Summary
• Dexter is a browser-based, domain-independent, explorer
for structured data (e.g. CSV, XML, JSON Databases,
APIs)
• Ad hoc exploration of structured data as tables through
Dexlog rules
• Client-side query evaluation
• Support for exporting, visualizing and sharing tables
• Implemented with Javascript — runs entirely inside user’s
browser
Project Page: http://dexter.stanford.edu

17. Backup Slides

18. DEXTER
Client-Side Rule Evaluation
• Hybrid-shipping strategy: Evaluate queries directly on
sources whenever possible
• Decompose queries
Input: q(X) :- source1.t1(X,Y) & source2.t2(Y,“a”)
Output: q(X) :- q1(X, Y) & q2(Y)
q1(X, Y) :- t1(X, Y) — evaluated at source1
q2(Y) :- t2(Y,“a”) — evaluated at source2
• Remove irrelevant rules
• Evaluate queries in parallel
http://dexter.stanford.edu

19. DEXTER
Additional Features
! Visualizing table’s data as charts ! Exporting into
popular formats
- CSV
- JSON
- XML
- RuleML/XML
! Sharing tables via Dexter Server
! Filters
http://dexter.stanford.edu