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--- 240:embobug [2013/04/27 13:09]
+++ 240:embobug [2021/12/29 16:21] (current)
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+====== MARC Review and MARC Global: 'Embedded booleans' ======
+Many years ago, we 'invented' a syntax that would make it easy to pack multiple reviews
+into a single statement. See below for the manual entry for this syntax.
+Although we are going to try to keep this way of doing things functional, we want to point out that in most cases, using PCRE regular expressions //(the new way of doing things)//, might be the better choice.
+For example, consider this 'embedded boolean':
+{{:240:embo1.png|}}
+Stringing together the starting numbers like this removes the need to make a separate pattern to match each number, and is a great improvement for the user. At runtime, though, the program splits these embedded patterns apart and runs the review just as if you had specified six different patterns:
+<code>
+TAG=082 SUBF=a DATA=^71 REGEX=True
+TAG=082 SUBF=a DATA=^72 REGEX=True
+TAG=082 SUBF=a DATA=^73 REGEX=True
+TAG=082 SUBF=a DATA=^74 REGEX=True
+TAG=082 SUBF=a DATA=^306 REGEX=True
+TAG=082 SUBF=a DATA=^646 REGEX=True
+</code>
+So, there is performance hit with this way of doing things. Perhaps a more efficient way to write this review would be to combine the first four patterns into one--
+<code>
+TAG=082 SUBF=a DATA=^7[1234] REGEX=True
+</code>
+--so that the program only has to run three reviews on each 082, instead of six.
+But now we have PCRE (which we did not have 20 years ago). And we can rewrite the above as simply:
+{{:240:pcre-version.png|}}
+PCRE uses parens to group **sub-patterns**((this, in itself, is reason alone to use PCRE; the old MARC Review syntax had no support for subpatterns at all)), and a single pipe to separate them from one another. To the software this appears as a single review, and as it isn't manipulated by our software at runtime, its much faster.
+It takes a bit of getting used to, but it should be worth it.
+----
+<code>EMBEDDED PATTERNS
+It is possible, and sometimes necessary, to specify multiple patterns in a single
+'DATA' pattern. This is done by stringing the patterns together, separating each
+one with one of the boolean symbols listed below.
+The following boolean symbols are supported within the DATA box:
+	&& = and
+	|| = or
+	!! = not
+You can use the following English equivalents for the above interchangeably, as long as
+they are enclosed in angle brackets (they are not case-sensitive):
+	<and>	= &&
+	<or>	= ||
+	<not>	= !!
+An example of each of these three boolean expressions follows.
+'And' example: 040 $d DLC<and>OCoLC
+	True if both 'DLC' and 'OCoLC' are present in $d in the same 040
+'Or' example: 035 $a OCoLC||TMQ
+	True if either 'OCoLC' or 'TMQ' are present in 035 $a
+'Not' example: 040 $d OCoLC<not>DLC
+	True if there is a $d 'OCoLC' and not a $d 'DLC' in the same 040
+These patterns can be combined with the standard Match Rules 'AND', and 'NOT'
+(eg. 'NOT 035 $a OCoLC||TMQ'). The Match Rule is applied AFTER the data is evaluated.
+NOTE: If you use a regular expression with an embedded boolean, it must be repeated for each
+argument. For example: 949 $a = '^PB<or>^PER' (The '^' is repeated before both PB and PER).
+</code>

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