Getting started

Tutorial

This session creates a database, loads a small materials ontology, changes it, and shows that the change survives a restart.

Create a database and load an ontology

Start the shell with a directory. OntoDB creates it if it does not exist.

$ ./build/dev/ontodb mydb
opened mydb: no snapshot; wal 0 records, 0 committed, 0 uncommitted dropped; 0 triples
OntoDB> \load data/tiny.owl
loaded 14 triples in 5.2 ms

data/tiny.owl is an OWL ontology in RDF/XML with four classes: Material, Metal, Alloy, and Polymer. The load is one transaction. When the line loaded 14 triples appears, those triples are on disk.

Query

A query may span lines. It runs when its braces close.

OntoDB> PREFIX m: <http://example.org/materials#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
SELECT ?kind WHERE {
  ?kind rdfs:subClassOf m:Material .
}
?kind
<http://example.org/materials#Metal>
<http://example.org/materials#Polymer>
(2 rows)

Alloy is not listed: it is a subclass of Metal, and OntoDB stores subClassOf as data, not as a rule to reason with.

Update

OntoDB> INSERT DATA { <http://example.org/materials#Ceramic> <http://www.w3.org/2000/01/rdf-schema#subClassOf> <http://example.org/materials#Material> . }
inserted 1 triple
OntoDB> \log 3
lsn 35 txn 2 term 18 <http://example.org/materials#Ceramic>
lsn 36 txn 2 update insert (18 9 4)
lsn 37 txn 2 commit
OntoDB> \quit

\log shows the transaction the insert wrote: a dictionary entry for the new IRI, the triple as three ids, and the commit.

Reopen

$ ./build/dev/ontodb mydb
opened mydb: no snapshot; wal 37 records, 2 committed, 0 uncommitted dropped; 15 triples
OntoDB> SELECT ?kind WHERE { ?kind <http://www.w3.org/2000/01/rdf-schema#subClassOf> <http://example.org/materials#Material> . }
?kind
<http://example.org/materials#Metal>
<http://example.org/materials#Polymer>
<http://example.org/materials#Ceramic>
(3 rows)

The open replayed the two committed transactions, the load and the insert.

Checkpoint and verify

OntoDB> \checkpoint
checkpoint at lsn 37: 18 terms, 15 triples; wal reset
OntoDB> \verify
snapshot: ok (lsn 37, 18 terms, 15 triples)
wal: ok (0 records, 0 bytes)
replay: matches the live database (15 triples)
invariants: ok (no duplicate triples, every id in the dictionary)
verify: ok

The checkpoint wrote a snapshot and emptied the log, so the next open loads the snapshot instead of replaying every record. \verify read both files back, rebuilt the database from them, and found it identical to the one in memory.

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