Our situation is that we need to import parametric shapes from competitors files. The layout of their screen and data fields are similar but different enough so that there is a conversion process. In addition we have over a half dozen competitor and maintenance would be a nightmare if done through code only. Since most of them use tables to store their parameters for their shapes we wrote a general purpose collection of objects to convert X into Y.
In my CAD/CAM application the file import is a Command. However the conversion magic is done by a Ruleset via the following steps.
- Import the data into a table. The field names are pulled in as well depending on the format.
- We pass the table to a RuleSet. I will explain the structure the ruleset in a minute.
- The Ruleset transform the data into a new set of objects (or tables) which we retrieve
- We pass the result to the rest of the software.
A RuleSet is comprise of set of Rules. A Rule can contain another Rule. A rule has a CONDITION that it tests, and a MAP TABLE.
The MAP TABLE maps the incoming field with a field (or property) in the result. There are can be one mapping or a multitude. The mapping doesn't have to involve just poking the input value into a output field. We have a syntax for calculation and string concatenation as well.
This syntax is also used in the Condition and can incorporate multiple files like ([INFIELD1] & "-" & [INFIELD2])="A-B" or [DIM1] + [DIM2] > 10. Anything between the brackets is substituted with a incoming field.
Rules can contain other Rules. The way this works is that in order for a sub Rule mapping to apply both it's condition and those of it's parent (or parents) have to be true. If a subRule has a mapping that conflicts with a parent's mapping then the subRule Mapping applies.
If two Rules on the same level have condition that are true and have conflicting mapping then the rule with the higher index (or lower on the list if you are looking at tree view) will have it's mapping apply.
Nested Rules is equivalent to ANDs while rules on the same level are equivalent of ORs.
The result is a mapping table that is applied to the incoming data to transform it to the needed output.
It is amicable to be being displayed in a UI. Namely a Treeview showing the rules hierarchy and a side panel showing the mapping table and conditions of the rule. Just as importantly you can create wizards that automate common rule structures.