A system we developed a while back for supporting multi-device context-aware queries. As low-level architectural support for context-aware comput-ing matures, we are ready to explore more general and powerful means of accessing context data. Information required by a context-aware appli-cation may be partitioned by any number of physical, organizational, or privacy boundaries. This suggests the need for mechanisms by which ap-plications can issue context-sensitive queries without having to explicitly manage the complex storage layout and access policies of the underlying data. To address this need, we have developedliquid, a prototype query service that supports distributed, continuous query processing of context data. This paper articulates the current need for such systems, describes the design of theliquid system, and presents both a room-awareness application and notification service demonstrating its functionality. Authors are Jeffrey Heer, Alan Newberger, Chris Beckmann, and Jason Hong

1. liquid
context-aware queries
chris beckmann
jeffrey heer
alan newberger
jason hong

2. liquid introduction
Context Fabric: storage and subscription
services at InfoSpace level
What about cross infospace concerns?
 “Give me the e-mails of all people in the room”
What about complex relations?
 “Give me all the people in the conference hall
with whom I have a co-author in common”

3. liquid introduction
 “Give me all the people in the conference hall
with whom I have a co-author in common”
Currently, a context-aware app must
handle all this complexity on its own!

4. liquid introduction
Enter liquid, a prototype query service
 distributed across infospaces
 location.occupantperson.email
 handles persistent, continuous queries
 people exiting, entering rooms
 supports rich set of data selection criteria
 selection, projection, joins

5. liquid concepts
entity type paths
 a naming mechanism for context data
query specification
 how to issue a query
query execution
 how a query is evaluated
result items
 encapsulation for query results

6. entity type paths
Each infospace in the sequence is specified by its
relation to the preceding infospace, and addressed by
an entity-link.
An entity type path specifies a ContextTuple to be retrieved at the end of a
sequence of infospaces.
location.occupant.publication

7. entity type paths
location.occupant.publication

8. entity type paths
location.occupant.publication

9. entity type paths
location.occupant.publication

10. query specification
 queries are specified using XML syntax
 future work: a high-level query language that
maps down to this intermediate XML rep.
<?xml version=“1.0” encoding = “UTF-8” ?>
<Query>
<QuerySpec persist=“true”>
<EntityTypePath>location</EntityTypePath>
</QuerySpec>
</Query>

11. query evaluation

12. result items
result items == collection of context tuples
+ query metadata (timestamp, status)
query result status types
 inserted new tuple inserted into an infospace
 deleted tuple deleted from an infospace
 updated tuple updated in infospace (and still matches query)
 exited tuple updated in infospace (and no longer matches)
 expired tuple fell out of window watched by liquid

13. future work
 testing / evaluation / deployment
 once confab deploys, this will be natural
 query language
 already have the basics of an OQL-like natural query
language, but need a parser
 perfect scope for an undergrad project
 advanced entity type paths
 intra-infospace scoping
 optimization
 making liquid faster, more robust in response to usage

14. conclusion
liquid provides distributed, continuous
queries over collected context data
a necessary component for enabling the
easy development of c/a-apps
as c/a-architectures deploy, liquid will
hopefully grow to match developers’
needs
liquid source code is bundled with the context fabric distribution
-check out package edu.berkeley.guir.confab.query
-context fabric home: http://sourceforge.net/projects/confab