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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: Are people really using Identity constraints specified in
 Roger, Good summary. CAM however is dastardly - in that it allows extensible function calls - to procedural code blocks - exactly for that backend integration. Of course both parties (sender / receiver) may need access to that - but CAM has a web service pluggable interface - that allows that. Having the declarative world call the procedural world imposes of course a constrained interaction model - so that the declarative model is not broken. Such calls are essential for answer realworld rule needs like - 'is quantity_ordered =< stock_on_hand' where the web service call to the ERP warehouse management system can answer this. Cheers, DW. ================================================================= Quoting "Roger L. Costello" <costello@m...>: > Hi Folks, > > An excellent, important discussion! Below I have summarized what I perceive > as the key issues. Comments are very welcome. > > Here are the two problems that we have been considering: > > Problem #1 > > A company has employees. The current company policy is that the minimum age > of employees is 16. What happens when a 15 year old whiz kid is hired? > Validation by the IT department of the data file for this new employee will > result in sending up error flags. Should the IT department run the > business, or should the business run the IT department? > > Problem #2 > > A person from the UK makes an online purchase from a US supplier. The online > supplier requires entry of a two-letter code in the "State" box and a > numeric value in the "postal code" box, despite the fact that the person > entered UK as the country. So, the person entered "ZZ" as the state and > 12345 as the postal code. Does validation result in forcing people to > supply incorrect information? > > In discussing these problems, two categories of validation were identified: > > 1. "Syntactical" or "structural" validation > 2. "Semantic" or "business rule" validation > > "Syntactical" or "structural" validation is useful in eliminating a certain > number of mechanical data entry errors, such as leaving out required items > or putting strings in fields that require numbers (e.g. phone numbers, > dates, etc.) > > "Semantic" or "business rule" validation captures some aspect of a business' > requirements. An example is validating that a credit card is acceptable. > > There are two categories of tools for doing validation: > > 1. Declarative-based tools > 2. Procedural-based tools > > The declarative-based tools include XML Schemas, XForms, CAM. The advantage > of these tools is that the constraints they express are easily changed. The > disadvantage is limited expressiveness (consequently, it may be very > difficult to express semantic/business rule constraints using these tools). > The declarative-based tools are typically client-side tools. > > The procedural-based tools include Javascript, Java, C#, etc. The advantage > of these tools is that they have rich expressiveness. The disadvantage is > that changes are not as easily made. The procedural-based tools are > typically back-end tools. > > The declarative-based tools are better suited for "Syntactical" or > "structural" validation. > > The procedural-based tools are better suited for "Semantic" or "business > rule" validation. > > Other Issues > > In a highly distributed system there is no definable "back-end" where all > business rules may be validated. In such a case, it may be beneficial to > push semantic/business rule validation out to the client-side. > > XML Schemas, XForms, CAM, Javascript - these are all a "means to an end". > > If you are going to validate, then validate! In Problem #2 the user was > forced to enter a 2-character state code, despite being from the UK. > Several people noted that the problem was not with too much validation, but > with not enough validation. If the system had been doing a good job > validating then "ZZ" would not have been allowed for the state code. > Further, full validation would have determined that if the country code is > UK then no value is required for the state code. > > /Roger > > > > ----------------------------------------------------------------- > The xml-dev list is sponsored by XML.org <http://www.xml.org>, an > initiative of OASIS <http://www.oasis-open.org> > > The list archives are at http://lists.xml.org/archives/xml-dev/ > > To subscribe or unsubscribe from this list use the subscription > manager: <http://www.oasis-open.org/mlmanage/index.php> > > 
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