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   Re: [xml-dev] Validation - Is it worth it ?

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  • To: xml-dev@lists.xml.org
  • Subject: Re: [xml-dev] Validation - Is it worth it ?
  • From: "Fraser Goffin" <goffinf@hotmail.com>
  • Date: Sat, 11 Feb 2006 12:39:55 +0000
  • Bcc:
  • In-reply-to: <43C04F3F.7070402@firmansyah.com>

Thanks Greg, some interesting points to consider.

I am mostly concerned with B2B. One of the issues I'm wrestling with is that 

a. the service contract is defined by an external standards body (we are but 
one implementer).
b. the data model that underpins the service operations are defined using 
XML schema and these reflect the broad business semantics for each operation 
(as agreed by a panel of contributors from our industry sector).
c. our business rules (in terms of what data content/structural constraints 
that would be acceptable) are less strict than the XML schema specifies (for 
example we may be tolerant of missing data).

So I guess I was considering whether we should validate according to our 
internal business rules rather than that of the externally defined contract, 
even when this can mean that a message received could be schema invalid 
(according to the industry standard definition) ?


>From: Greg Hunt <greg@firmansyah.com>
>To: Fraser Goffin <goffinf@hotmail.com>,  xml-dev@lists.xml.org
>Subject: Re: [xml-dev] Validation - Is it worth it ?
>Date: Sun, 08 Jan 2006 10:31:11 +1100
>I know that "be liberal in what you accept and strict in what you emit" is 
>firmly embedded in the race memory now, but I am not sure that that applies 
>to the technical aspects of B2B type transactions.
>Why do you want to process messages that "may" be processable?  If you keep 
>in mind a distinction between technical processes and business processes, 
>there is less doubt.  Technically acceptable messages should enable the 
>business process.  Acceptance of the message should mean that there is a 
>business process that will handle the message.  Rejection of the message 
>should indicate technical issues.  Anything else is probably not scalable 
>in terms of effort  and in terms of guaranteed processing time.  It seems 
>to come down to whether the business rules for fixing the message data can 
>be defined and used.  We need to be careful that we are not also fixing the 
>semantics of the messages that we receive.
>If there are business rules that define the changes to data content that 
>are acceptable then there is no doubt about whether the message can be 
>processed, what is in doubt is whether in the end you get a business 
>transaction (money) out of it.
>If there are technical issues with a message, if the received structure is 
>wrong or unexpected for some reason, then the semantics are also in doubt 
>and passing what is probably machine generated data to a person to resolve 
>an issue involves asking that person to decide whether this is a bug or 
>something unexpected in the mind of a programmer.  It is easier and more 
>reliable to ask the originator what is going on than it is to ask a human 
>to interpret a broken XML structure for, for example, a purchase order 
>(meaning that I am not sure that you can always push the message to a 
>person to have them look at it in a scalable, business-meaningful way).
>If this is B2B type traffic, who pays for getting the semantics of the 
>message wrong?  If you receive a value transaction from someone and "fix" 
>it in some technical and non-trivial way, who now pays for the transaction? 
>  Is the cost of sending and receiving the message so high that the time 
>and effort of a human and the associated risk of further error is 
>Fraser Goffin wrote:
>>Recently I've been involved in building a validation process using a 
>>combination of schema based and rules (schemaTron) and it got me thinking 
>>about how much validation is the right amount.
>>The 'type' of validation processing I'm talking about is that which might 
>>be performed at a B2B gateway and is perhaps better categorized as 
>>'technical' validation (ie. basic structural conformance and some content) 
>>rather than business rules (although the distinction is pretty thin).
>>>From the business perspective, it is undesirable to reject any message 
>>thus lose an opportunity to complete a transaction. So from this point of 
>>view one might imagine that validation at this stage should be minimal, 
>>perhaps not even full schema (or perhaps a 'more relaxed' version of the 
>>published interface). This might be justified on the basis that rules, 
>>perhaps in a business process engine or application logic, are better at 
>>determining whether a message is business processable or not. Plus one can 
>>always push messages to a manual process and let a human decide !
>>On the flip side, we want to protect the integrity of our operational 
>>systems from erroneous data and, perhaps the most obvious reason, 
>>validation can provide an optimization of the process in the sense that, 
>>when the interaction is asynchronous (and possibly long running), it may 
>>be preferable to let a caller know right away that a message has some 'bad 
>>data' rather than for them to find that out some time later after having 
>>received an initial acknowledgement of receipt.
>>To me this highlights the conundrum of a desire for strongly typed 
>>[service] interfaces versus the looser coupling and tolerance to change 
>>that we also typically seek. I am trying to find the 'sweet spot' that 
>>allows through messages that 'may' be processable, but rejects those where 
>>even if directed to a manual (human workflow) process would still not be 
>>worth the effort. I sometimes refer to this as 'compatible' messages 
>>versus enforcing strict adherence to a technical specification.
>>I also have noted that versioning service interfaces (or even just XML 
>>schemas) can be somewhat problematic and can exacerbate validation issues, 
>>and to some extent mitigates against using them for validation purposes, 
>>particularly if they haven't been designed with any extensibility 
>>mechanisms at all to accommodate 'non breaking' change (e.g. 
>>Some of you may be thinking 'is there a question here anywhere ?', sorry I 
>>have meandered on somewhat. What I'm really after is finding out what 
>>others have found to be a good approach to message validation and whether 
>>there are views about how to achieve a balance between optimizing business 
>>opportunity and rejecting 'junk mail'.
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