Oct. 27, 1995:	Update; negative time intervals eliminated with add. condition
		in where clause of insert/delete
Oct. 28, 1995:	Update; 'nonsequenced valid update ..' fuer valid/bitemp. tables
Nov. 1, 1995:	Views; syntax changed, disallowing temp. spec 'as valid' etc
Nov. 2, 1995:	Referential integrity; get_reference_data/4 expanded (Myrach)
Nov. 2, 1995:	Meta-Data; changed dbinit-file, added TimeDB-meta-table-data to
		table_types and table_view_schemes 
Nov. 2, 1995:	Meta-Data; switched long-type field 'query' with field 'type' in
		meta-table 'assertions' 
Nov. 2, 1995:	Referential integrity; added check if tables are temp. compatible for
		RI-check 
Nov. 23, 1995:	Version 1.01, Primary Key check added
		New demo26; changed demo43 due to primary key check 
Nov. 30, 1995:	check_faktor_type(intersect(I1, I2), ...) in check.pl; Int1/Int2 added
		instead of term interval/2 in check_exp_type (Myrach)
Dec. 08, 1995:	Table- and column-constraints added (parser, translate, check, evaluate,
		metadata, constraints changed):
		translate_from/7 added, case []+[T-A-TT1|Rest]
		get_column_constraints/7 etc. adapted
		alter table statement enhanced in parser und translate
Dec. 12, 1995:	Version 1.03
		demo14 added
Feb. 7, 1996:	Missing error message for invalid_set_values added to errors.pl. 
		Transaction and valid time mixed up in 'NONSEQUENCED VALID UPDATE'-
		statement; changed get_sel_where/8 in translate.pl, in case of
		tt-snapshot-[] and tabletype bitemporal.  
Feb. 8, 1996:	Renamed file meta.pl to interface.pl	
Feb. 9, 1996:	Added implicit coalescing for or-expressions
		Changed generate_or_list/4 in file translate.pl
Mar. 18, 1996:	Changed behaviour of transaction and bitemporal tables when
		table is altered: transaction time is set to [now-until changed).
		Changed change_meta_info/8 in translate.pl
Mar. 19, 1996:	Added flag VALID <exp> for queries, deletes, updates, inserts
		Known problem: valid updates with subqueries
		Syntax of assertions changed
Mar. 21, 1996:	Renaming of valid time column for VIEWS changed (rename_columns1/3 in
		translate.pl)
		Changed SQL3 period string to PERIOD '[...)' (interval_to_internal/4 in
		calendar.pl)
Mar. 22, 1996:	No propagation of tuc into derived tables! (Changed table_coal/3 in
		parser.pl)
Mar. 25, 1996:	Semantics of TUC delete and update changed. Every tuple valid sometime 
		in [now-forever) gets modified (not only those overlapping 'now').
		Changed translate_man/4 in translate.pl.
April 15, 1996:	Version 1.04	
Sept. 30, 1996:	Bug: Conditions in subqueries using OR lead to an error in calculate_union/2;
		changed calculate_union/2 in evaluate.pl.
		Version 1.05
Oct. 25, 1996:	ATSQL2 Syntax changed wrt. ANSI/ISO-proposal: VALIDTIME, TRANSACTIONTIME,
		valid-time table definition with AS VALIDTIME PERIOD(DATE)
		Version 1.06
Nov. 1, 1996:   Bug in parser (superfluous error message); changed interval_primary/1
                Version 1.07
