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database#
View page sourceThe Dismod_at Database Tables#
Primary Key#
If table_name is a table (in this database), its first column
has name table_name _ id
that is the primary key for the table.
The values in this column are integer
,
start at zero and increment by one for each row in the table.
Name Column#
Suppose that table_name is a table (in this database),
and the column table_name _ name
exists.
In this case, the values in this column are text
must be unique;
i.e., the names can act as substitutes for the primary key.
The names are intended to be easier for a human to remember than the ids.
Foreign Key#
If this is the name of a table its primary key is
the column this _ id
.
If this primary key is used in another table it is
called a foreign key (in the other table).
The name of the column in the other table will be this _ id
or it will end with _ this _ id
.
A value in the foreign key column must also appear in the
corresponding primary key column, or it must be null
.
parent#
Note that the column parent is a primary
key value for the node table ; i.e, node_id
.
Note that this column is not named node_id nor does it end
in _ node_id .
This is not an exception because the parent
column is itself
in the node
table and hence this is not a foreign key.
Null#
It is an error for a value to be null
unless the documentation for the corresponding column specifies
a meaning for this case.
Lower and upper bounds are an exception to this rule (see below).
Bounds#
If a lower (upper) bound is null
,
it is interpreted as minus (plus) infinity.
Integer#
The minimum integer (negative integer with the largest absolute value)
is used to represent a null
integer value in a table.
An error message will be generated if
the minimum integer appears in a table that is read by dismod_at.
Text can be Null, not Empty#
The empty string is used to represent a null
text value in a table.
An error message will be generated if the empty string
appears in a text field that is read by dismod_at.
Real Can be Null, not Nan#
If a real value is null
, it is represented as nan
.
An error message will be generated if
the value nan
appears in a table that is read by dismod_at.
Type Names#
The types in this database are integer
, real
and
text
. The type names INTEGER
, REAL
, and TEXT
can also be used.
Contents#
Name |
Title |
---|---|
input |
|
data_flow |
Comment Columns and Tables#
Any table (in this database) may have any number of columns with names that begin with the two characters
c_
. These are comment columns and are ignored bydismod_at
. In addition, tables with a names beginning withc_
are also considered comments and are ignored bydismod_at
.