WPOTD: Project code names

WPOTD stands for "Wiki Page Of The Day". This is going to be a label for when I find interesting wiki pages. There's not going to be any kind of schedule for this, but I'll post them as I run across them.

I just so happened to run a across an interesting one today. I was looking for a schema to follow for computer names. Examples of this would include super heroes, planets, beers, etc. My search landed me on

http://en.wikipedia.org/wiki/List_of_computer_technology_code_names

It is a listing of names used for projects from various companies like Microsoft, Intel, and Apple.

The 5 Biggest Mistakes Made by an LLC Business

I was just reading this article and found it interesting. It listed the following as the 5 biggest mistakes made by an LLC:

1. Before the LLC Business Entity is Formed, Don't Conduct Business.
2. Failing to Actually Issue Ownership Interests of the LLC Business Entity.
3. Failing to Create a Management Structure and Appoint Officers for the LLC Business Entity.
4. Failure to Get Investment Obligations in Writing.
5. Thinking that an LLC Business is a Foolproof Layer of Liability Protection.

Load Balancing Software

I was talking to one of our system admins the other day about load balancing. He suggested I look into HAProxy. Apparently, gifts.com uses this for their load balancing rather than a hardware layer. One of the features I'm looking for is the ability to handle sticky sessions. I didn't see anything about it on the home page, but it's suppose to support it. This is something I'd like to look into at a later time:

http://haproxy.1wt.eu/

List of commands

I ran across a nice page of linux commands. Some of them I already knew, but there were several that were new to me.

http://www.pixelbeat.org/cmdline.html

spotlight on the command line

I've recently learned about mdfind on OSX. mdfind is essentially a commandline interface to Spotlight. One of the benefits of using mdfind over locate is that the indexing is done in real time. As soon as the file is added to the file system, it is added to the index.

You can read up on the command at:
http://macdevcenter.com/mac/2006/01/04/mdfind.html

Sending screen commands

You can start a detached screen session using the following command:


screen -dm -S myTest


This will create a screen session named 'myTest'. You can verify it was created with 'screen -list'. You should see something similar to the following when you type that command:


$ screen -list
There is a screen on:
31306.myTest (Detached)
1 Socket in /tmp/uscreens/S-mmasters.


Then you can send commands to the newly created screen session:


screen -S myTest -p 0 -X stuff 'top^M'


You have to type <control-v><control-m> to get the ^M character correctly. This command will essentially type 'top' and 'enter' in the screen session named 'myTest' for the 0th window. When you reconnect to the screen session, you should see top running. You can type 'q' to quit top.

The important part of this command is the -X. This switch can take several different commands. You can see all the commands available at

http://www.gnu.org/software/screen/manual/screen.html#Command-Summary

I found this link to be very helpful.

Validating xml and xsd with xmllint

Recently, I've been going through some tutorials on XSD. I always find the tutorials on W3Schools to be very help and they've come through on this subject. The information on their site is concise and to the point. While going through their tutorials, I wanted to find an easy way of testing what I'd learned. Preferably, this would involve a command line utility.

I found that xmllint provides the functionality I was looking for. I'd like to step through what I've been doing to test my XML/XSD validation.

1. Create the XSD file. I'll use an example from W3Schools. Save the following to a file named note.xsd:

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
       targetNamespace="http://www.w3schools.com"
       xmlns="http://www.w3schools.com"
       elementFormDefault="qualified">

<xs:element name="note">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="to" type="xs:string"/>
      <xs:element name="from" type="xs:string"/>
      <xs:element name="heading" type="xs:string"/>
      <xs:element name="body" type="xs:string"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>

</xs:schema>

2. Create the XML file. Again, we'll use an example from W3Schools. Save the following to a file named note.xml:

<?xml version="1.0"?>
<note xmlns="http://www.w3schools.com"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.w3schools.com note.xsd">
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>

3. Validate the XML against the Schema. You will need to have xmllint installed. I type the following on the command line for validation:

xmllint --noout --schema note.xsd note.xml

This gives me the following output:

note.xml validates


Now that we know what happens for passing validation, I'd like to show you a failing one. Let's change the order of the elements in our XML. This will cause the validation to fail because the order is explicit per our XSD. The following XML switches the to and from elements:

<?xml version="1.0"?>
<note xmlns="http://www.w3schools.com"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://www.w3schools.com note.xsd">
 <from>Jani</from>
 <to>Tove</to>
 <heading>Reminder</heading>
 <body>Don't forget me this weekend!</body>
</note>

This will give the following output when we run xmllint:

note.xml:5: element from: Schemas validity error : Element '{http://www.w3schools.com}from': This element is not expected. Expected is ( {http://www.w3schools.com}to ).
note.xml fails to validate


I'm a little disappointed with the error message that I receive, but I think I'll gain a better understanding of them as I use the tool more.