Compositions of refinement
Types of compositions
Nog is two foreign keys, connecting three tables:
refering fields are in one intermediate table.
create table a (
id num primary key,
data float
);
create table b (
id num primary key,
ref1 num references a(id), -- important
ref2 num references a(id), -- ballast
ref3 num references c(id), -- important
ref4 num references c(id), -- ballast
data float
);
create table c (
id num primary key,
data float
);
Refinement consist of two fields, listed through colon:
field, refering to previous section ("a"), is specified first;
field, refering to next section ("c"), is specified second
(refering fields can have identical name).
Syntax of nog consist of three section and looks so:
Buckle is two foreign keys, connecting three tables:
refering fields refer to one intermediate table.
create table a (
id num primary key,
ref1 num references b(id), -- important
ref2 num references b(id), -- ballast
data float
);
create table b (
id num primary key,
data float
);
create table c (
id num primary key,
ref1 num references b(id), -- important
ref2 num references b(id), -- ballast
data float
);
Syntax of buckle consist of three section and looks so:
Crossroad is two foreign keys,
connecting two tables in opposite directions:
one refering field is in one table and refers to primary key of second table,
other refering field is in second table and refers to primary key of first table.
create table a (
id num primary key,
ref num references b(id),
data float
);
create table b (
id num primary key,
lnk num references a(id),
data float
);
There exist two not equivalent syntax of crossroad
(each consists of two sections).
Branching is two foreign keys, connecting three tables:
refering fields refer to one surrounding table
create table a (
id num primary key,
data float
);
create table b (
id num primary key,
ref1 num references a(id), -- important
ref2 num references a(id), -- ballast
data float
);
create table c (
id num primary key,
ref1 num references a(id), -- important
ref2 num references a(id), -- ballast
data float
);
(syntax of branching:)
.a.(b#ref1 c#ref1). -- both "b" and "c" are required
.a.(b#ref1 | c#ref1). -- "b", or "c", or both are required
... or refering fields are in one surrounding table
create table a (
id num primary key,
ref1 num references b(id), -- important
ref2 num references b(id), -- ballast
ref3 num references c(id), -- important
ref4 num references c(id), -- ballast
data float
);
create table b (
id num primary key,
data float
);
create table c (
id num primary key,
data float
);
(syntax of branching:)
.a#ref1+ref3.(b c). -- both "b" and "c" are required
.a#ref1^ref3.(b | c). -- "b", or "c", or both are required
Continuation is two foreign keys, connecting three tables:
refering fields refer to two surrounding tables
create table b (
id num primary key,
data float
);
create table c (
id num primary key,
data float
);
create table d (
id num primary key,
ref1 num references b(id), -- important
ref2 num references b(id), -- ballast
ref3 num references c(id), -- important
ref4 num references c(id), -- ballast
data float
);
(syntax of continuation:)
.(b.d#ref1 c.d#ref3). -- both "b" and "c" are required
.(b.d#ref1 | c.d#ref3). -- "b", or "c", or both are required
... or refering fields are in two surrounding table
create table b (
id num primary key,
ref1 num references d(id), -- important
ref2 num references d(id), -- ballast
data float
);
create table c (
id num primary key,
ref1 num references d(id), -- important
ref2 num references d(id), -- ballast
data float
);
create table d (
id num primary key,
data float
);
(syntax of continuation:)
.(b#ref1 c#ref3).d. -- both "b" and "c" are required
.(b#ref1 | c#ref3).d. -- "b", or "c", or both are required
Combined key
Если внешний ключ состоит из нескольких полей,
то в детерминации ссылающиеся поля перечисляются через знак умножения.
If foreign key consist of several fields,
then these fields is listed in refinement through sign of multiplication.
P.S.
Article is guide to implement ideas of
p.39-48 of
pdf-document.
Dima Turin, dmitryturin@yandex.ru