CHAPTER 1: Introduction

Table 1-1
 

Typographical Conventions
Examples	Description
CALL  THEN	In the syntax definition of the command, words in upper case are keywords. These are not case-sensitive and may consist of a mixture of upper case and lower case when typed into Empress.
tabinst  attr	Items in lower case italics refer to categories. When typed into Empress, appropriate substitutions of actual names or expressions must be used. For example, personnel for table. Within text, they appear in bold typeface.  Note that for user-defined names, case is significant and must be typed exactly as originally defined.
|item 1|  |item 2|	Items stacked between vertical lines " | " are options from which one must be chosen.
[ ]	Square brackets are used to indicate that the items enclosed are optional.
{ }	Braces may contain more than one item or none at all.
SELECT command	When a command is referred to in the text (anywhere other than in the syntax) of the manual, it will usually be written in upper case.

Table 1-2
 

Typographical Conventions - Keyboard Keys
Examples	Description
<Return>	Keys on your keyboard appear in between angled brackets.
<Ctrl+A>	Key chords which require pressing more than one key at a time appear with a "+" separating the keys.

All text in a script between "/*" and "*/" is considered a comment and is ignored. A comment may span multiple lines.

Semicolons (;) are optional everywhere except in the Parameter, External, Global and Local Variable Definitions. Quotes (single or double) are required for literal strings; they may not enclose variables. Quotes should also be used around names of windows, fields, tables and attributes to preclude confusion with keywords.

Note

However, quotes should not be used around names of procedure scripts.

In general, Empress 4GL interprets words without quotes as either keywords, variables, numbers or functions. Words within quotes are interpreted as literals.

Warning

Do not name variables or subscripts after them.
 

database	is the name of the current default database. This database is searched for any table references where the table name is not preceded by a database name. The values can be changed to make another database the current default database.
error_string	is the most recent user trappable error.
error_number	is the unique number identifying error_string.
got_records	is a flag giving the status of the last next_rec, prev_rec, next_record or prev_record calls.      The variable has the following values: 1 successful 0 unsuccessful; no next or previous record -1 record was unattainable
insert_mode	determines whether the Field Editor is in insert mode. Set it to 0 to put the Field Editor in replace mode and any integer value to put it in insert mode. Pressing the Insert mode key in the Field Editor sets the variable to 1.
interrupt_number	is the signal number for most recent user trappable interrupt.
records_selected	is the number of records selected in the last SELECT statement (with the COUNT option in effect).
record_status	is a flag giving the status of the last next_rec, prev_rec, next_record, prev_record, next_line, prev_line, next_group or prev_group calls. The values of record_status are as follows:    -2 Error -1 Record is locked 0 no next/previous record 1 Got next/previous record 2 Beginning of group. This value is only set with next_rec and next_record. 3 Aggregate Record
screen_row	is the number of rows on the terminal screen.
screen_column	is the number of columns on the terminal screen.
mouse_row	is the current row position of the mouse cursor.
mouse_column	is the current column position of the mouse cursor.
touch_row	is the row where the touch screen was last touched.
touch_column	is the column where the touch screen was last touched.

1.3 The NULL Keyword

The NULL keyword can be used to check if a variable, attribute or field is null, and to assign a null value to a variable, attribute or field.

A variable is null when it is declared, and a field is null when it is empty.

Note that NULL means that a variable has no determinable value. In a comparison, if one term is a variable with a null value, the expression will return false, unless the other term is the keyword NULL.

For example, the expression "if variable 1 = variable 2" returns false even if both variable 1 and variable 2 are null.

You have to check for null values explicitly.

Warning

Do not name variables or subscripts after them.

1.5 Expressions

expr is:

| attr                                |

| string CONSTANT                     |

| number                              |

| (expr)                              |

| CONVERT expr [TO] data type         |

| CONVERT expr [TO] GENERIC data type |

| expr CONVERT TO data type           |

| expr CONVERT [TO] GENERIC data type |

| expr operator expr                  |

| expr operator                       |

| operator expr                       |

| built_in_function                   |

| user_defined_function               |

| user_defined_set_function           |

| set_function                        |

| math_library_function               |

Notes

1. Implicit data type conversions occur during the evaluation of expressions whenever possible.
2. Unless the result of an expression is explicitly converted to a data type, the result is generic data (data not governed by data type parameters and not associated with any attribute). Generic data is discussed in the "Data Types" chapter of Empress SQL Reference manual.
3. Explicit conversion to data types is discussed in the Empress SQL User's Guide.
4. The use of expressions for date arithmetic is described in the Empress SQL User's Guide.
5. An error message will be returned if an expression is impossible to evaluate, for example, if it requires division by zero.

1.6 Data Types

Table 1-3
 

Type	Descriptions	Example
CHAR	A sequence of characters that may be letters, numbers, or other symbols.	abcde12345xyz
DATE	A date in one of the formats acceptable to Empress SQL.
DECIMAL	A sequence of digits, followed by a decimal place and trailing digits.	12345.678
FLOAT	Also known as "scientific notation". A digit followed by a decimal point and trailing digits, followed by "e" and an exponent of ten.	1.2345e2
INTEGER	A generic integer.

1.7 Command Summary Groups

• Variable Declarations
• Control Statements
• Database Statements
• System Functions
• Administrative Functions

Do not name variables, subscripts or user-defined functions after them.

1.7.1 Variable Declarations

Table 1-4
 

Name	Description
parameter	define variable passed to the script
external	define external variable
global	define global variable
local	define local variable

1.7.2 Control Statements

Table 1-5
 

Name	Description
call	call a function or procedure
call application	calls an Empress 4GL application
call emprepwr	call an Empress Report Writer script
display	display field value
disable interrupt	disable trapping of system interrupt signals
enable interrupt	reactivate trapping of system interrupt signals
exit	leave the application
export	export Empress 4GL data structure
if	branch depending on condition
import	import Empress 4GL data structure
let	assign a value
on error	trap error and respond
on interrupt	trap interrupt signal and respond
return	leave a function, optionally returning a value
switch	branch depending on value
while	repeat while a condition is true

1.7.3 Database Statements

Table 1-6
 

Name	Description
cancel	cancel or rollback the current transaction
check	validate compatibility with attribute
close	close a table
commit	commit the current transaction
define select	define a select without executing
delete	delete record from table
disable	disable update operations on context
enable	enable update operations on context
end_select	remove a context
insert	insert record into table
lock	lock a table
next_group	get the next group from context
next_rec	get next record from context
next_record	get the next record from context
open	open a table
prev_group	get the previous group from context
prev_rec	get previous record from context
prev_record	get the previous record from context
rollback	rollback a transaction
savepoint	set save point in transaction
select	select from tables giving a context
select context	refresh a predefined context
start transaction	start a transaction
undefine	cancel a define select
update	update record in table

1.7.4 System Functions

Table 1-7
 

Name	Description
attr_update	update an attribute with a value
attr_value	return the current value of an attribute
beep	make the terminal beep
check_field	check the validity of data in a field
clear_fields	clear the fields in a window
clear_save_value	clear saved value
clear_status	clear status window
compare_save_value	compares saved field with current field value
current_field	make a field current
current_field_name	return the name of the current field
current_field_number	return the number of the current field
current_field_update	update the current field with a value
current_field_value	return the value of the current field
current_field_video	change the video of the current field
current_window	make a window current
current_window_name	return the name of the current window
debug_message	print a message and pause
define_group_multi	associate a context with a window for multiple record displays generated by SELECT statements with the GROUP BY option.
define_multi	associate a context with a window
display_page	display a page in a multi-record display
empsql	invokes the Query Language interface
error_message	enter error state and print a message
error_window	associate a window and field to display the error messages
field_help_window	display field help window through a command
field_mode	change the mode of a field
field_update	update a field with a value
field_value	return the current value of a field
field_video	change the video of a field
get_save_value	return the saved value of a field
info_message	print a message and continue
info_window	associate a window and field to display the message
key_context_name	return the key context name on the stack
key_name	return the key name for a key label
key_script	execute a key script
largest_field_number	return the size of a multiple field
mouse_field_name	return the mouse field name
mouse_field_number	return the mouse field number
mouse_key_down	return mouse key pressed data
mouse_location	return the current mouse location
mouse_window_name	return the mouse window name
move_window	move a window on the screen
next_field	go to next field of the current window
next_line	get next line in multi-record display
next_page	get next page in multi-record display
pop_key_context	pop a key context for a window
prev_field	go to previous field of current window
prev_line	get previous line in multi-record display
prev_page	get previous page in multi-record display
print_screen	print the screen
push_key_context	push a key context for a window
remove_window	remove a window
reset_fields	reset fields to default values
reset_key_context	reset the key context stack
restore_field	sets fields to their saved field values
save_field	save current field value
scroll_page	scroll a multi-record display
scroll_window	scroll a window over a form
set_attr_values	copy values from fields to attributes
set_field_values	copy values from attributes to fields
set_key_values	copy values from key labels to fields
set_save_value	copy value to save field value
show_window	show a window on the screen
sys_command	execute an operating system function and return
sys_prompt	display Y/N question in a pop-up window
sys_value	execute command returning result
sys_variable	return value of an environment variable
system	call the operating system
temporary_window	display a window and wait for keystroke
touch_field_name	return the touch screen field name
touch_field_number	return the touch screen field number
touch_location	update the touch screen location
touch_window_name	return touch window name
zoom_window	grow or shrink a window

1.7.5 Administrative Functions

Warning

The following function names are used in Empress 4GL Development Environment sys_main application (for Empress 4GL internal use only). Do not name user defined functions after them:

Table 1.7
 

Name	Description
compile_application	compile an application
compile_definition	compile a definition
compile_script	compile a script
copy_form	copy a form
copy_script	copy an application
create_application	create an application
create_default	create a default application
create_menu	create a menu
debug_mode	turn the 4GL debugger on or off
delete_form	delete a form
delete_script	delete an application
edit_form	invoke the form editor
link_application	link an application
load_definition	load a definition
rename_form	rename a form
rename_script	rename an application

1.8 Script Definition

    [parameter [;]]

    [external [;]]

    [global [;]]

    [local [;]]

    {statement [;]}

A statement may be a control statement, a database statement, a system function or an administrative function. Control statements determine the flow of control within an application. Database statements concern actions involving access to databases. System functions concern actions involving access to windows and fields. Administrative functions concern actions involving access to scripts, applications, forms and Application Generator definitions. Most of the administrative functions are for Empress 4GL internal use.

To access Empress tables, the tables must be "opened" in the application. When a table is opened it may be assigned a new name, giving a table instance. There may be several instances of the same table (i.e., the table is "opened" to several names) in an application.

To access records in a table, a SELECT is done on a table instance. This produces a group of records called a context. Once you have a context, you can get the next or previous record in this context, giving you a current record.

A record may be created by assigning values to attributes. To update or delete a record you must have a current record in a context. A record may be inserted, updated or deleted by referencing the appropriate table instance.

Note

There is a restriction that applies to database access. Any table instance can support only one context of records at a time.