How to read dotted decimal diagrams
In dotted decimal format, each syntax element is written on a separate line. If two or more syntax elements are always present together (or always absent together), they can appear on the same line, as they can be considered as a single compound syntax element.
Each line starts with a dotted decimal number, for example 3
or 3.1
or 3.1.1.
To
hear these numbers correctly, make sure that your screen reader is
set to read out punctuation. All the syntax elements that have the
same dotted decimal number (for example, all the syntax elements that
have the number 3.1
) are mutually exclusive alternatives.
For example, if you hear the lines 3.1 USERID
, 3.1
SYSTEMID
, you know that your syntax can include either USERID
or SYSTEMID
,
but not both.
The dotted decimal numbering level denotes the
level of nesting. For example, if a syntax element with the dotted
decimal number 3
is followed by a series of syntax
elements with the dotted decimal number 3.1
, all
the syntax elements numbered 3.1
are subordinate
to the syntax element numbered 3
.
Characters
such as commas that are used to separate a string of syntax elements,
are shown in the syntax just before the items they separate. They
might appear on the same line as each item, or on a separate line
with the same dotted decimal number as the relevant items. The line
might also show another symbol giving information about the syntax
elements; all these symbols are explained below. For example, the
lines 5.1* ,
, 5.1 LASTRUN
, 5.1
DELETE
mean that if you use more than one of the syntax elements LASTRUN
and DELETE
,
they must be separated by a comma. If no separator is given, assume
that you use a blank to separate each syntax element.
If a
syntax element is preceded by the %
symbol, this
indicates a reference that is defined elsewhere. The string following
the %
is the name of a syntax fragment, rather than
a literal. For example, the line 2.1 %OP1
means that
at this point, you should refer to the separate syntax fragment OP1
. OP1
,
in the syntax from which this example was taken, gave a list of further
options.
Certain words and symbols are used next to the dotted
decimal numbers to add information about the syntax elements. Occasionally,
these words and symbols might occur at the beginning of the element
itself. For ease of identification, if the word or symbol is a part
of the syntax element, it is preceded by the escape character, which
is a \ (backslash). For example, the *
symbol can
be used next to a dotted decimal number to mean that this syntax element
can be repeated. If a syntax element actually starts with the *
symbol,
for example a syntax element * FILE
with the dotted
decimal number 3, it is given in the format 3 \* FILE
.
If the format is 3* FILE
, this means that there is
a syntax element FILE
, which can be repeated. If
the format was 3* \* FILE
, this means that there
is a syntax element * FILE
, which can be repeated.
The words and symbols used next to the dotted decimal numbers are as follows:
-
?
means an optional syntax element. If a dotted decimal number is followed by the?
symbol, this means that all the syntax elements with that dotted decimal number, and any subordinate syntax elements that they each have, are optional. If there is only one syntax element with that dotted decimal number, the?
symbol appears on the same line as the syntax element, for example5? NOTIFY
. If there is more than one syntax element with that dotted decimal number, the?
symbol appears on a line by itself, followed by the syntax elements that are optional. For example, if you hear the lines5 ?
,5 NOTIFY
,5 UPDATE
, you know that the syntax elementsNOTIFY
andUPDATE
are optional; you can choose one or none of them. The?
symbol is equivalent to a bypass line in a railroad diagram. -
!
means a default syntax element. If a dotted decimal number is followed by the!
symbol, appended to the last digit of the dotted decimal number, this means that this syntax element is the default of all the elements with the same dotted decimal number. Only one of the syntax elements that share the same dotted decimal number can specify a!
. For example, if you hear the lines2? FILE
,2.1! (KEEP)
,2.1 (DELETE)
, you know that(KEEP)
is the default option for theFILE
keyword. If you include theFILE
keyword but do not state your choice of option, the default optionKEEP
is applied. As well as the particular syntax element marked with the!
symbol, the default also applies to the next higher dotted decimal number. In the example above, the default applies to2? FILE
as well as to2.1! (KEEP)
, meaning that if you omit the wordFILE
, the defaultFILE(KEEP)
is used. However, you might instead hear the lines2? FILE
,2.1
,2.1.1! (KEEP)
,2.1.1 (DELETE)
. As the default only applies to the next higher dotted decimal number, which in this case is2.1
, it does not apply to2? FILE
. In this case, if you omit the wordFILE
, nothing is used. -
*
means a syntax element that is optional and can be repeated. If a dotted decimal number is followed by the*
symbol, this means that this syntax element it is optional, and can be repeated. For example, if you hear the line5.1* data-area
, you know that you can include more than one data area, or you can include none. If you hear the lines3*
,3 HOST
,3 STATE
, you know that you can includeHOST
,STATE
, both, or nothing. Note that if a dotted decimal number has an asterisk next to it, and there is only one item with that dotted decimal number, you can repeat that same item more than once. If a dotted decimal number has an asterisk next to it, and several items have that dotted decimal number, you can use more than one item from the list, but you cannot use the items more than once each. In the example above, you could writeHOST STATE
, but you could not writeHOST HOST
. The*
symbol is equivalent to a loop back line in a railroad syntax diagram. -
+
means a syntax element that must be included at least once, and can be repeated. If a dotted decimal number is followed by the+
symbol, this means that this syntax element must be included at least once, and can be repeated. For example, if you hear the line6.1+ data-area
, you know that you must include at least one data area, and you can include more than one. If you hear the lines2+
,2 HOST
,2 STATE
, you know that you must includeHOST
,STATE
, or both. As for the+
symbol, you can only repeat a particular item if it is the only item with that dotted decimal number. The+
symbol, like the*
symbol, is equivalent to a loop back line in a railroad syntax diagram.
Click to hear this description again.
Click to return to text in How to read syntax diagrams.