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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: RE: evolvable formats
 10/10/2002 5:33:19 AM, "bryan" <bry@i...> wrote: Referring generally to http://lists.xml.org/archives/xml-dev/200210/msg00583.html but not quoting at length. I am not an RSS weenie, but I am very interested in it as a case study in "evolveable formats", i.e., how real users deal with the cruel reality that application-level XML standards are produced slowly, by political and interpersonal processes that seldom yield fully satisfactory results, and which are obsolete the day they are cast in a schema and/or given a namespae :-). XML doesn't fix human frailty, it just reduces the technological overhead that hid human issues behind syntax and interoperability problems (e.g., EDI standards AFAIK). FWIW, I take away the following lessons from the RSS 0.9x/1.0/2.0/3.0/etc. experience (which again I'm happy not to have lived through), and would appreciate some responses from people who lived through it firsthand. 1 - Politics happens, Evolution is continuous, deal with it. With technology, as best you can. Don't make technology choices that are fragile in the face of human nature. 2 - Namespaces - work best for mixing instances of well-defined vocabularies/schemas together, they don't work so well to support evolution or un-typed XML. Schema evolution using namespaces is a Known to Be Hard, TAG-level problem. If you want to leverage commonly deployed code that understands a specific namespace (XHTML, SVG, etc.), the full-blown Namespaces in XML is your friend, well Real Soon Now anyway. If you just want to disambiguate tags, it has lots of little gotchas (that "RSS 2.0" seems to have been gotten by!) that make it a challenge for people who don't grok its subtleties. (MOST OF THE REAL WORLD!!!) If NS for XML is overkill for you and your users, steal its great idea of leveraging DNS to disambiguate tags, but in a more Desperate Perl Hacker or home-brew parser friendly way. For example, <rant class="xegesis.org">Why oh Why oh Why oh Why!!!! </rant> is distinct from all other "rant" elements using this convention, is easy to handle with regexp or bare-bones well-formed XML, but won't fall afoul of "real" NS-aware software. or <em class="www.w3.org/1999/xhtml"> Stay away from all the messy verbosity of a URI if you don't NEED it to be a URI</em> This tells someone downstream that you mean the HTML "em" tag, not something else. A real browser will quietly ignore it on display. Someday Real Soon Now an AF-NG architecture map can be used to aid its processing by generic software :-) 3 - If you don't know exactly what you're dealing with, heuristics beat logic. If the tag is <table> and it has HTML table elements inside it, it's probably an HTML table! Don't throw it away because it's in the wrong namespace. 4 - If you're going to claim to use an XML technology, do it properly. If you're using angle brackets to make regexp parsers easier to write, don't use XML idioms (especally colons!!!) half-way. 5 - If you really don't need XML, don't fool with it. Well-formed XML has the advantage of letting you deal with hierarchical,labelled data in a way that leverages all sorts fo other tools. If all you have is name-value pairs (i.e., 99.99% of the RSS I've seen) something like RSS 3 makes an awful lot of sense. If you're rolling your own tools and not leveraging XML tools, ask yourself what value XML offers you or your users. (Hint: WikiML is a LOT easier to author than XML ... RSS 3.0 is a one-line parser in Python, Perl (?), etc.) I guess this is more of a question: 6 - Why on earth would one even THINK about using entity-encoded non-well-formed HTML in a syndication format??? Use the HTML tags, but close them! Use tidy to clean up the junk you get from your users! Why fool with any alternative? Even if you're taking the advice in point 5, just "escape it" with an HTML: line label or whatever. Someone downstream will thank you. Again, these are starting points for discussion by an outsider, not advice from one claiming these are design patterns or best practices Thoughts? 
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