{"id":645,"date":"2014-06-28T20:30:29","date_gmt":"2014-06-29T01:30:29","guid":{"rendered":"http:\/\/tiemensfamily.com\/TimOnCS\/?p=645"},"modified":"2014-06-28T20:30:29","modified_gmt":"2014-06-29T01:30:29","slug":"computer-science-hard-things","status":"publish","type":"post","link":"https:\/\/tiemensfamily.com\/timoncs\/2014\/06\/28\/computer-science-hard-things\/","title":{"rendered":"Computer Science Hard Things"},"content":{"rendered":"

There is a popular saying about Computer Science (see here<\/a> and here<\/a>):<\/p>\n

There are only two hard things in Computer Science: cache invalidation and naming things.<\/p>\n

— Phil Karlton<\/p><\/blockquote>\n

There is a funny variation that makes it “There are only two hard problems in Computer Science: cache invalidation, naming things, and off-by-one errors.”<\/p>\n

I propose there are actually three hard things:<\/p>\n

    \n
  1. Naming things<\/li>\n
  2. Cache invalidation<\/li>\n
  3. Dependency resolution<\/li>\n<\/ol>\n

    My criteria for being a “hard thing”:<\/p>\n

      \n
    1. Must be applicable to multiple scopes<\/li>\n
    2. Must not be fully solved<\/li>\n<\/ol>\n

      Examined this way, it is interesting to see why these are the three deserve to be on the list:<\/p>\n

        \n
      1. Naming things\n
          \n
        1. Applicable to every area in computer science – variable names, class names, machine names, network names, security policy names, URIs<\/a>, etc. It even applies to this list: think of the difference between naming the first item “cache invalidation” versus just “caching”.<\/li>\n
        2. Not at all solved. You can barely say we have good heuristics for this.<\/li>\n<\/ol>\n<\/li>\n
        3. Cache invalidation\n
            \n
          1. Applicable to multiple layers of computer hierarchy: CPU registers, L1, L2, L3, etc., disk caches, network resource caches, DNS caches, etc.<\/li>\n
          2. Solved in the sense we know it is a balancing act between efficiency and correctness. Not solved for the general case, however. If there even is a “general case” at all.<\/li>\n<\/ol>\n<\/li>\n
          3. Dependency resolution\n
              \n
            1. Applicable to multiple domains: run-time (think Dependency Injection), build time (think Apache Ivy and Maven), hardware-software, distributed systems, and probably more<\/li>\n
            2. Solved in the sense we know about topological sorting<\/a> to help with transitive dependencies.
              \n For run-time, the entire sub-field of dependency injection has multiple solutions:               Spring Framework<\/a>, Guice<\/a>, PicoContainer<\/a>. Does anybody remember DLL Hell<\/a>? That shows that “API definition” (which is a candidate for its own “Hard Thing” entry) is a sub-problem of dependency resolution.
              \n For build time, the better build systems make it easy to specify your dependencies and add               global exclusions<\/a> to get you out of transitive dependency issues.
              \n For hardware-software, think about the hardware requirements for running a particular application or installing a particular driver.
              \n For distributed systems, think about (for example) your application requires which version of which database. For provisioning, has been partially solved by               Chef<\/a> and Puppet<\/a> and others. For detection, still very much roll-your-own.\n <\/ol>\n<\/li>\n<\/ol>\n

              So, did I create any converts? Do you agree there are 3 Hard Things in Computer Science?<\/p>\n","protected":false},"excerpt":{"rendered":"

              There is a popular saying about Computer Science (see here and here): There are only two hard things in Computer Science: cache invalidation and naming things. — Phil Karlton There is a funny variation that makes it “There are only … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[5],"tags":[],"_links":{"self":[{"href":"https:\/\/tiemensfamily.com\/timoncs\/wp-json\/wp\/v2\/posts\/645"}],"collection":[{"href":"https:\/\/tiemensfamily.com\/timoncs\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/tiemensfamily.com\/timoncs\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/tiemensfamily.com\/timoncs\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/tiemensfamily.com\/timoncs\/wp-json\/wp\/v2\/comments?post=645"}],"version-history":[{"count":0,"href":"https:\/\/tiemensfamily.com\/timoncs\/wp-json\/wp\/v2\/posts\/645\/revisions"}],"wp:attachment":[{"href":"https:\/\/tiemensfamily.com\/timoncs\/wp-json\/wp\/v2\/media?parent=645"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/tiemensfamily.com\/timoncs\/wp-json\/wp\/v2\/categories?post=645"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/tiemensfamily.com\/timoncs\/wp-json\/wp\/v2\/tags?post=645"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}