DES 2.6 Released

[fernan]

[Apologies for multiple receptions]

Hello.
This is a mail just for informing that the new release 

  Datalog Educational System version 2.6 
  http://des.sourceforge.net

has been launched on October, 26th, 2011, and ported to

  GNU Prolog 1.4.0

Current version introduces several enhancements. A novel one 
includes a proposal for hypothetical SQL queries which allow 
to assume extra tuples in existing relations (either tables 
or views). Such queries are useful, for instance, in decision 
support systems as they allow to submit a query by assuming 
some knowledge which is not in the database. Also, top-n SQL 
queries are included, following ISO 2008, as well as the 
other common form TOP. The metapredicate top/2 is also added 
to Datalog with the same aim of restricting the number of 
tuples in the answer  of any goal. Supported SQL has been 
extended to cope with SQL statements in any legal part of the 
projection list (as, e.g., components of arithmetic 
expressions). Although performance is not the target of this 
educational system, hash indexing has been added to the 
extension table, therefore speeding-up computations. Syntax 
error reports and time displays have been enhanced, as well 
as help on commands and built-ins, and hints on them for 
misspelled entries. TAPI has been extended for some commands. 
Several new commands have been added; in particular /check_db 
which allows to get a consistency report on a database. 

A complete list of enhancements, changes and fixed bugs is attached 
to the end of this message. 
Please, see http://des.sourceforge.net for details.

  Best regards.


==============================================================
Fernando Saenz Perez
Profesor Titular de Universidad / Associate Professor
Home Page: http://www.fdi.ucm.es/profesor/fernan
Tel: + 34 913947642. Fax: + 34 913947547
Despacho / Office: 435 (4ª planta / 4th floor)
Dept. Ingenieria del Software e Inteligencia Artificial / 
Department of Software Engineering and Artificial Intelligence
Universidad Complutense de Madrid
Facultad de Informatica
C/Profesor Jose Garcia Santesmases, s/n
E - 28040 Madrid. Spain
==============================================================



Version 2.6 of DES (released on October, 26th, 2011)

* Enhancements:
  o A novel proposal for hypothetical SQL queries which allow to assume extra 
tuples in existing relations (either tables or views)
  o New SQL Top-N queries following ISO 2008 (another common form TOP N is also 
supported)
  o New Datalog built-in top/2 for computing Top-N queries, i.e., those with 
the number of tuples in the answer limited to N
  o SQL statements are allowed in the projection list, even as components of 
arithmetic expressions
  o Anonymous variables are discarded from the answer schema should they occur 
in queries, views and autoviews (even in heads)
  o New sub-graph algorithm for finding predicate dependency graphs restricted 
to queries. It replaces an older one with exponential complexity, which did 
consulting and/or querying some small programs to raise memory exhaust 
exceptions
  o Display of predicate dependency graph is ordered
  o Display of strata is first ordered by strata and then by predicate
  o Running info display about number of inferred tuples, working with console 
and windows applications
  o Datalog built-ins distinct/1 and distinct/2 also work for arbitrary 
queries, not only for atoms
  o Enhanced solving performance by hash-indexing of extension table
  o Enhanced time displays. Time is formatted as either milliseconds (MS) (MS 
ms.) for less than a second; or seconds (SS) and milliseconds (MS) (SS.MS s) 
for less than a minute; or minutes (MM), seconds and milliseconds (MM:SS.MS) 
for less than an hour; or hours, minutes, seconds and milliseconds (H:MM:SS) 
for greater than or equal to an hour
  o Case-insensitive interactive user answers (debugging, test cases, ...)
  o Keyboard interrupt caught for SWI-Prolog distributions. This allows 
interrupt the current computation without exiting DES
  o Syntax error report on incompatible relation schemas in set operations
  o Syntax error report about mismatch type for condition in metapredicate 
group_by
  o Added hints on misspelled commands
  o Help on commands and built-ins
  o Hints on misspelled entries for:
    + Existing commands /debug_datalog and /trace_datalog
    + New commands /pdg
  o Enabling TAPI for the next existing commands and synonyms:
    + /consult
    + /reconsult
    + /cd
    + /pwd
  o New commands:
    + /check_db Check database consistency w.r.t. declared integrity 
constraints (types, existency, primary key, candidate key, foreign key, 
functional dependency, and user-defined). Display a report with the outcome
    + /display_answer Display whether display of computed tuples is enabled
    + /display_answer Switch Enable or disable display of computed tuples (on 
or off, resp.) The number of tuples is still displayed
    + /hypothetical Display whether hypothetical SQL queries are allowed
    + /hypothetical Switch Enable or disable hypothetical SQL queries (on or 
off, resp.) 
    + /indexing Display whether hash indexing on extension table is enabled
    + /indexing Switch Enable or disable hash indexing on extension table (on 
or off, resp.) Default is enabled, which shows a noticeable speed-up gain in 
some cases
    + /pdg PredName Display the current predicate dependency graph restricted 
to the first predicate found with name PredName
    + /pdg PredName/Arity Display the current predicate dependency graph 
restricted to the predicate with name PredName and Arity 
* Changes:
  o Constraints assertions are not checked when disabling constraint checking
* Fixed bugs:
  o Integrity constraint checking could not be changed. Bug introduced in 
version 2.4
  o Syntax error exceptions when consulting files exited DES
  o A FROM-less SQL statement in a series of local view definitions of a WITH 
statement was not parsed
  o SQL parsing involving non-existent column names tweaks for discarding 
incorrect statements and accept correct statements 
  o The command /abolish deleted rules of view definitions but not the schema
  o Datalog rule listings with added parentheses enclosing disjunctions when 
needed
  o Some nested SQL statements containing expressions were not parsed
  o SWI-Prolog distributions included incorrect computation time displays when 
detailed timing was enabled
  o Some unsafe rules involving set variables were not transformed when safety 
transformation was enabled
  o Use of set variables in equalities and is/2 always yielded to error 
messages, although the use were correct