Re: [Help-glpk] Database connectivity in MathProg

[glpk xypron]

ello Andrew!

>
> Here is my proposals.
>
> In general case the input table to be read from a database has the
> following syntax (some elements may be omitted):
>
>    table t IN "..." : [ i ~ I, j ~ J, ... ] s <- [k ~ K, ...],
>       p[...] ~ P, q[...] ~ Q, ... ;
>
> where t is a symbolic name of the data table; i, j, k, ... are dummy
> indices; I, J, K, ... are column names for dummy indices; s is a set;
> p, q, ... are symbolic names of parameters; P, Q, ... are column names
> for parameters.

The use of [ i ~ I, j ~ J, ... ] is unclear to me. k ... are the index 
parameters of set s{k, ....}.

>
> The statement 'read table' is equivalent to the following query:
>
>    select I, J, K, ..., P, Q from ...
>
> Once a next record has been read from the database, values of I, J, K,
> ... are assigned to the dummy indices i, j, k, ..., the corresponding
> n-tuple is added to set s, indexing expressions are evaluated, and
> values P, Q, ... are assigned to corresponding members of parameters
> p, q, ... .
>
> The output table to be written to a database has the following syntax:
>
>    table t { ... } OUT "..." : expr ~ A, expr ~ B, ... ;
>
> where { ... } is a domain, expr, ... are arbitrary expressions, and
> A, B, ... are column names.
>

I would rather stick to:

    table t OUT "..." : { ... } -> [k ~ K], expr ~ A, expr ~ B, ... ;

The domain, expr, ... may have multiple indices. These indices are needed as 
columns for the SQL table to be written. When creating the SQL table they 
should become key columns.

{ ... } can be a set:   s{k, ...}

> The statement 'write table' is equivalent to the following:
>
>    drop ...
>    create ...
>    insert into ... (A, B, ...) values(...)
>    insert into ... (A, B, ...) values(...)
>    . . .
>
> Expressions are evaluated over the specified domain and their values
> are assigned to corresponding columns.

For the reduced scope to be implemented this is correct.

AMPL used the drop, create, insert sequence only if the disposition of all 
columns of a write table is OUT. In other cases missing columns are added as 
needed and existing data is only updated but not deleted.

I guess in SQL multiple lines can be inserted with a single INSERT statement. 
Hence all values should be passed to the C handler routine at once.

Best regards

Xypron
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