Tolog Updates

tolog updates
TMRA 2009, November 12, Leipzig
Lars Marius Garshol, <larsga@bouvet.no>

Why an update language?
Easier to use than the API
empowers new groups of users
Potentially better performance than the API
Can be embedded in various DSLs
Architectural benefits
enables JDBC-like API
easily accessible over the network

Why one based on tolog?
TMQL was not ready at the time
in fact, it still isn’t
We have a tolog implementation
implementing the query part is the biggest job
So tolog was the pragmatic choice

What it contains
INSERT: add new data to topic map using CTM
DELETE: remove data from topic map
MERGE: merge objects
UPDATE: change existing values

The language

DELETE
Static form
delete lmg
Dynamic form
delete $person from instance-of($person, person)

Deletion effects
Deleting topic removes
from scope
from topic types
objects typed with
as reifier
Topic map
Topic
Name
Variant
Occurrence
Association
Role

Delete functions
Used for removing values from set properties
delete subject-identifier(topic, “http://ex.org/tst”)
delete item-identifier(topic, “file://...#tst”)
delete subject-locator(topic, “http://ex.org”)
Other functions
scope($statement, $topic)
reifies($reified, $reifier)
direct-instance-of($topic, $type)

MERGE
Static form
MERGE topic1, topic2
Dynamic form
MERGE $p1, $p2 FROM instance-of($p1, person), instance-of($p2, person), email($p1, $email), email($p2, $email)

INSERT
Static form
INSERT lmg isa person; - “Lars Marius Garshol” .
Dynamic form
INSERT tmcl:belongs-to-schema(tmcl:container : $s, tmcl:containee: $c) FROM instance-of($c, tmcl:constraint)

Another INSERT example
INSERT $topic $psi . FROM instance-of($topic, $type), instance-of($type, psi-type), topic-name($topic, $name), value($name, $value), str:translate($value, $token, ..., ...), str:concat($psi, “http://psi.example.org/...”)

Yet another
INSERT event-in-year(event: $e, year: $y) FROM start-date($e, $date), str:substring($y, $date, 4)

Ugliness with INSERT
Other statements can use %parameter% syntax
in INSERT this is not possible in the CTM part
have to say FROM $a = %a% to translate
May need to project away variables used in query but not in CTM
right now this is done via an implicit projection
not clear whether this will confuse users or not

UPDATE
Static form
UPDATE value(@3421, “New name”)
Dynamic form
UPDATE value($TN, “Ontopia”) FROM topic-name(oks, $TN)

The UPDATE functions
value($object, $string)
works on topic name, variant, occurrence
resource($object, $string)
works on variant and occurrence

Considerations

New API
Old API has QueryProcessorIF methods
QueryResultIF execute(String)
ParsedQueryIF parse(String)
New API adds
int update(String)
ParsedModificationStatementIF parseUpdate(String)
also adds ParsedStatementIF as common interface

New access methods
Omnigator query plug-in
being extended to support updates
TMRAP web service
being extended with a tolog-update request

A scripting language?
Considering to make a language supporting batches of statements
that is, running series of modification statements
perhaps also setting variables
Not clear what features are needed
for loops? if? etc

Implementation
Mostly straightforward...
new classes to represent parsed versions of new statements
all reference the class for SELECT statements for their FROM subqueries
...except CTM parsing
requires two different Antlr parsers (CTM & tolog)
had to split the query string in advance, then pass different pieces to different parsers

Concerns
Is it expressive enough?
just about any modification can be expressed
however, it might require many statements
Do INSERT statements need “if”?
to handle missing values, for example
Rules and templates
currently, these cannot be defined in modification statements
is that a bug? or a feature?

Current status
All four statement types implementated
Test suite added
Some minor nits still need sorting out

Future work
Start using the language
Write documentation!
Hand it over to users
See how it goes

Tolog Updates

by Lars Marius Garshol

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