{"id":1216,"date":"2005-12-29T21:50:00","date_gmt":"2005-12-30T01:50:00","guid":{"rendered":"http:\/\/www.markbaker.ca\/wp\/2005\/12\/29\/mandatory-tolerance\/"},"modified":"2005-12-29T21:50:00","modified_gmt":"2005-12-30T01:50:00","slug":"mandatory-tolerance","status":"publish","type":"post","link":"http:\/\/www.markbaker.ca\/blog\/2005\/12\/mandatory-tolerance\/","title":{"rendered":"Mandatory tolerance"},"content":{"rendered":"

Phil Windley summarizes<\/a>\na point by Dion Hinchecliffe;<\/p>\n\n

\nI spoke with Dion yesterday and he talked to me about governance mistakes he sees clients making. The number one problem is something he called the “tyranny of the `MUST understand’ flag.” You get a SOAP-based Web service loaded up with WS-* header elements all tagged ‘MUST understand’ and you end up with something every-bit as much a central command and control structure as if you’d just reintroduced the mainframe. No one can do anything unless they’re using the same toolset.\n<\/blockquote>\n\n

I think I understand the issue here, but I think there’s more to it than\nyou might extract from that paragraph.<\/p>\n\n

First off, mandatory extension mechanisms like\nmustUnderstand<\/a>\nare a Good Thing, because it makes messages more self-descriptive; if<\/em> a message\nis extended in such a way that older processors can’t accurately interpret the\nmessage, then you need it to save those processors from processing a message\nwhich they can’t process.<\/p>\n\n

That said though, there needs to be recognition that there’s a fairly high\ncost of deployment of these kinds of extensions because each one that’s defined\nbasically bifurcates the space of interoperable agents (you know, just like\ndeploying a new service interface does … but that’s another issue 8-).<\/p>\n\n

And that’s where I agree with Dion. If you find yourself using mustUnderstand\nin more than a handful of your interactions, chances are that you’ve messed up\nsomewhere, likely by failing to account for sufficient extensibility in previous\nversions. In fact, I’d even extrapolate from that to suggest that if you’re using\nmustUnderstand in version 1.0 of your system, and that system is closed (i.e. behind\na firewall, or otherwise not interacting with pre-existing software), you’ve\ndefinitely<\/em> screwed up.<\/p>\n\n

Speaking of which… Perhaps the worst offender in this regard is\nWS-Addressing<\/a>,\nbecause it effectively mandates the use of at least one mandatory extension in every\nmessage; wsa:To. Well, technically it doesn’t require<\/em> that it be tagged as\nmandatory, but I think it’s pretty obvious that if a recipient didn’t understand\nwhere the message was addressed, that all hell would break lose if it tried to process\nit. So, if you use WS-Addressing, then all of your messages are prima facie\nunprocessable by all existing SOAP software<\/em>. Oopsie!<\/p>","protected":false},"excerpt":{"rendered":"Phil Windley summarizes a point by Dion Hinchecliffe; I spoke with Dion yesterday and he talked to me about governance mistakes he sees clients making. The number one problem is something he called the “tyranny of the `MUST understand’ flag.” You get a SOAP-based Web service loaded up with WS-* header elements all tagged ‘MUST […]","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[26],"class_list":["post-1216","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-soap"],"_links":{"self":[{"href":"http:\/\/www.markbaker.ca\/blog\/wp-json\/wp\/v2\/posts\/1216","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.markbaker.ca\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.markbaker.ca\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.markbaker.ca\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.markbaker.ca\/blog\/wp-json\/wp\/v2\/comments?post=1216"}],"version-history":[{"count":0,"href":"http:\/\/www.markbaker.ca\/blog\/wp-json\/wp\/v2\/posts\/1216\/revisions"}],"wp:attachment":[{"href":"http:\/\/www.markbaker.ca\/blog\/wp-json\/wp\/v2\/media?parent=1216"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.markbaker.ca\/blog\/wp-json\/wp\/v2\/categories?post=1216"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.markbaker.ca\/blog\/wp-json\/wp\/v2\/tags?post=1216"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}