XML 2.0

December 4th, 2010

First for the record, I’m speaking only for myself, not my employer, the W3C, Apple, Google, Microsoft, WWWAC, the DNRC, the NFL, etc.

XML 1.1 failed. Why? It broke compatibility with XML 1.0 while not offering anyone any features they needed or wanted. It was not synchronous with tools, parsers, or other specs like XML Schemas. This may not have been crippling had anyone actually wanted XML 1.1, but no one did. There was simply no reason for anyone to upgrade.

By contrast XML did succeed in replacing SGML because:

  1. It was compatible. It was a subset of SGML, not a superset or an incompatible intersection (aside from a couple of very minor technical points no one cared about in practice)
  2. It offered new features people actually wanted.
  3. It was simpler than what it replaced, not more complex.
  4. It put more information into the documents themselves. Documents were more self-contained. You no longer needed to parse a DTD before parsing a document.

To do better we have to fix these flaws. That is, XML 2.0 should be like XML 1.0 was to SGML, not like XML 1.1 was to XML 1.0. That is, it should be:

  1. Compatible with XML 1.0 without upgrading tools.
  2. Add new features lots of folks want (but without breaking backwards compatibility).
  3. Simpler and more efficient.
  4. Put more information into the documents themselves. You no longer need to parse a schema to find the types of elements.

These goals feel contradictory, but I plan to show they’re not and map out a path forward.
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Could not load a dependent class com/jcraft/jsch/Logger

June 25th, 2010

Have you ever seen an Ant error message like this?

/Users/elharo/Projects/XOM/build.xml:545: Problem: failed to create task or type scp
Cause: Could not load a dependent class com/jcraft/jsch/Logger
       It is not enough to have Ant's optional JARs
       you need the JAR files that the optional tasks depend upon.
       Ant's optional task dependencies are listed in the manual.
Action: Determine what extra JAR files are needed, and place them in one of:
        -a directory added on the command line with the -lib argument

Do not panic, this is a common problem.
The commonest cause is a missing JAR.

This is not a bug; it is a configuration problem

As usual, the ant error message is completely unhelpful, though for once it’s at least technically correct. (Most of the time when ant says, “This is not a bug; it is a configuration problem”, it is in fact a bug and not a configuration problem.) Here’s what’s really happening.
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Dn’t Abbrvt

April 28th, 2010

Is req a request or a requisition?

Is res a response, a reservation, a resume, or a result?

Is def a default or a definition?

Is rng a range or a random number generator?

Is v1 version 1 or value 1?

Is e an event, an entity, or an exception?

Is f a file or a float?

Is lst a list or the least value?

Is temp a temporary variable or a temperature reading?

Is rep a representation, a representative, a repetition, or a reputation?

Is tm a time or a trademark? Or even another temporary variable? And if it is a time, is it a timestamp, a time of day, or a duration? (These are three very different things.)

Is admin an administrator, an administrative assistant, or a system administrator?

In context, you can usually figure these things out, but you have to think about them. That’s inefficient. Far better to just spell out what you mean from the get go.
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Bruce Eckel is Wrong

April 20th, 2010

Every time the subject of checked versus runtime exceptions comes up, someone cites Bruce Eckel as an argument by authority. This is unfortunate, because, as much as I like and respect Bruce, he is out to sea on this one. Nor is it merely a matter of opinion. In this case, Bruce is factually incorrect. He believes things about checked exceptions that just aren’t true; and I think it’s time to lay his misconceptions to rest once and for all.

Let’s see exactly what Bruce’s mistake is. The following is an extended selection from Thinking in Java, 4th edition, pp. 490-491:

An exception-handling system is a trapdoor that allows your program to abandon execution of the normal sequence of statements. The trapdoors used when an “exceptional condition” occurs, such that normal execution is no longer possible or desirable. Exceptions represent conditions that the current method is unable to handle. The reason exception-handling systems were developed is because the approach of dealing with each possible error condition produced by each function call was too onerous, and programmers simply weren’t doing it. As a result, they were ignoring the errors. It’s worth observing that the issue of programmer convenience in handling errors was a prime motivation for exceptions in the first place.

One of the important guidelines in exception handling is “Don’t catch an exception unless you know what to do with it.” In fact, one of the important goals of exception handling is to move the error-handling code away from the point where the errors occur. This allows you to focus on what you want to accomplish in one section of your code, and how you’re going to deal with problems in a distinct separate section of your code. As a result, your mainline code is not cluttered with error-handling logic, and it’s much easier to understand and maintain. Exception handling also tends to reduce the amount of error-handling code, by allowing one handler to deal with many error sites.

Checked exceptions complicate the scenario a bit, because they force you to add catch clauses in places where you may not be ready to handle an error. This results in the “harmful if swallowed” problem:

try {
// ... to do something useful
} catch (ObligatoryException e) {} // Gulp!

Do you see the mistake? It’s a common one. Read the rest of this entry »

Would You Entrust Your Data to These Yokels?

December 31st, 2009

You have asked Firefox to connect
securely to www.delldatasafe.com, but we can't confirm that your connection is secure.

Normally, when you try to connect securely,
sites will present trusted identification to prove that you are
going to the right place. However, this site's identity can't be verified.
What Should I Do?

If you usually connect to
this site without problems, this error could mean that someone is
trying to impersonate the site, and you shouldn't continue.

             www.delldatasafe.com uses an invalid security certificate.

The certificate is not trusted because the issuer certificate is unknown.

(Error code: sec_error_unknown_issuer)

If Dell can’t even manage their public key certificates, how can I trust them to keep my data safe and secure?
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