Syntactical Conventions
To keep this chapter as readable as possible, we have chosen to omit some details that are irrelevant for practically all &-modelers. In the very rare case that these technicalities are of interest, the reader could have a look in the sourcecode of the parser, where all EBNF statements are in comments.
Purpose
This page is meant as a reference for syntactical details and conventions, reserved words, etc.
Learning the syntax
The most effective way to learn Ampersand's syntax is to copy from existing scripts. This is learning by examples. This reference chapter is suitable to check things, and less suitable for learning.
Symbols
Ampersand has reserved words, such as RELATION
, CONTEXT
, CONTAINS
. All reserved words are written in capital letters. They are introduced on the fly. You will find an exhaustive list of reserved words at the end of this page.
Untyped atoms are written between double quotes, e.g. "Peter"
or "KD-686-D"
. If you want to introduce a double quote inside an atom, escape it with a backslash, e.g. "the symbol \" is called double quote"
.
Numeric atoms always start with a digit, e.g. 4711
or 75.88E3
. The boolean atoms are TRUE
and FALSE
. Dates and timestamps follow the Excel-syntax, e.g. ??? The atom _SESSION
indicates the current user session, and is an instance of concept SESSION
. It is used in services.
Brackets must always match. For terms, we use round brackets (
and )
. For populations and services we use square brackets [
and ]
.
Constructs that contain ampersand statements are contexts and patterns. They always come in pairs: PATTERN
and ENDPATTERN
, and CONTEXT
and ENDCONTEXT
.
White space characters (spaces, tabs, CRLF) are meaningless. You can use them freely to layout your script in a way that helps you to recognize its structure.
A comment on a single line starts with --
. Everything after a --
symbol is ignored until the line ends. Multiline comments are wrapped between comment brackets {-
and -}
. Multiline comments may be nested.
Identifiers always start with a letter. Concepts start with a capital letter, as in Person
, Case
, A
, and Order
. Relation names start with a lower case letter, as in contains
, attr
, sessionLogin
, or r
.
terms
terms are combined with operators. Binary operators may require brackets to avoid ambiguity. To save writing unneccessary brackets, some precedence rules are in place.
operator category | precedence | operators |
logic | 1 (weakest) | |- (subset), |
binary boolean | 2 |
|
binary relational | 3 |
|
unary prefix, unary postfix | 4 (strongest) |
|
Within an operator category, you must place brackets to disambiguate. E.g. r/\s\/t
is not allowed. You have to write either (r/\s)\/t
or r/\(s\/t)
. Across categories, you may omit brackets because a higher precedence binds stronger. So r;s\/t
means (r;s)\/t
. (Note that (r;s)\/t
and r;(s\/t)
have different meanings). Associative operators (\/
, /\
, ;
) need not be disambiguated with brackets. So r\/s\/t
and (r\/s)\/t
and r\/(s\/t)
all mean exactly the same.
List of reserved words
Keywords in Ampersand are always written in CAPITALS.
Keywords for relations
PRAGMA
UNI
INJ
SUR
TOT
SYM
ASY
TRN
RFX
IRF
PROP
CONTAINS
Keywords for rules
RULE
MESSAGE
VIOLATION
TXT
SRC
TGT
I
V
ONE
ROLE
MAINTAINS
Keywords for services
INTERFACE
FOR
LINKTO
BOX
Keywords for identities
Keywords for views
VIEW
ENDVIEW
DEFAULT
TEMPLATE
HTML
Keywords for generalisations:
CLASSIFY
ISA
IS
Keywords for TType:
REPRESENT
TYPE
ALPHANUMERIC
BIGALPHANUMERIC
HUGEALPHANUMERIC
PASSWORD
BINARY
BIGBINARY
HUGEBINARY
DATE
DATETIME
BOOLEAN
INTEGER
FLOAT
AUTOINCREMENT
Reserved words for values of atoms:
TRUE
FALSE
--for booleans_SESSION
Reserved words for concepts
ONE
SESSION
Experimental keywords:
SERVICE
EDITS
Deprecated keywords:
SPEC
KEY
PROCESS
ENDPROCESS
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