Example: music schema

The music schema (schema.sql) is from an example in the paper “Relational lenses: a language for updatable views”

tracks1

track	date	rating	album	quantity
Trust	2018	5	Wish	5
Lovesong	2018	5	Galore	1
Mysong	2018	5	Galore	1
Lullaby	2018	3	Show	3

An update strategy for tracks2

An update strategy on the view tracks2 by using Datalog (tracks2.dl):

% describe the schema of sources and views
source tracks1('TRACK':string,'DATE':int,'RATING':int,'ALBUM':string,'QUANTITY':int).
view tracks2('TRACK':string,'RATING':int,'ALBUM':string,'QUANTITY':int).

% rule for deletion from tracks1
-tracks1(TRACK,DATE,RATING,ALBUM,QUANTITY) :- tracks1(TRACK,DATE,RATING,ALBUM,QUANTITY),
    not tracks2(TRACK,RATING,ALBUM,QUANTITY).

+tracks1(TRACK,DATE,RATING,ALBUM,QUANTITY) :- tracks2(TRACK,RATING,ALBUM,QUANTITY),
    not tracks1(TRACK,_,RATING,ALBUM,QUANTITY), tracks1(TRACK,DATE,_,ALBUM,_).

+tracks1(TRACK,2018,RATING,ALBUM,QUANTITY) :- tracks2(TRACK,RATING,ALBUM,QUANTITY),
    not tracks1(TRACK,_,_,ALBUM,_).

Verifying and compiling the update strategy into SQL statements saved in the file (tracks2.sql):

birds -v -f tracks2.dl -o tracks2.sql

An update strategy for tracks3

An update strategy on the view tracks3 over the view tracks2 by using Datalog (tracks3.dl):

% describe the schema of sources and views
source tracks2('TRACK':string,'RATING':int,'ALBUM':string,'QUANTITY':int).
view tracks3('TRACK':string,'RATING':int,'ALBUM':string,'QUANTITY':int).

% constraints:
⊥() :- tracks3(T,R,A,Q), NOT Q>2.

% view definition:
% tracks3(T,R,A,Q) :- tracks2(T,R,A,Q),Q > 2.

% rule for insertion to tracks2
+tracks2(TRACK,RATING,ALBUM,QUANTITY) :- tracks3(TRACK,RATING,ALBUM,QUANTITY),
    not tracks2(TRACK,RATING,ALBUM,QUANTITY), QUANTITY > 2.

% rule for deletion from tracks2
-tracks2(TRACK,RATING,ALBUM,QUANTITY) :- tracks2(TRACK,RATING,ALBUM,QUANTITY),
    not tracks3(TRACK,RATING,ALBUM,QUANTITY), QUANTITY > 2.

Verifying and compiling the update strategy to SQL statements saved in the file (tracks3.sql):

birds -v -f tracks3.dl -o tracks3.sql