.NET/ASP.NET/C#/VB.NET PDF Document SDK

Four well-known relational database systems available today that work on both Windows and Unix operating systems are MySQL, PostgreSQL, Oracle, and SQLite. Each has significantly different features from the others, and therefore has different uses.

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When you create the Call to Action slide shown on the upper left in Figure 9-34, place the dartboard graphic at the center, and duplicate the dart twice so that you have three darts to rotate and position at the bull s eye. Leave the headline hidden as you verbally relate the point, Aim for three goals, and you ll hit the marks you want. For the Key Point (Bene t) slides (upper right, lower left, and lower right), apply a split-screen custom layout as described in 8, using a Picture placeholder on the right half of the slides for the photographs. On the left half of the custom layout, include the dart and bull s eye to sustain that visual element through the presentation at these most important slides. The dartboard and dart are also elements that t naturally into a navigational bar through the corresponding Explanation and Detail slides. It will be a nice touch to leave your audience with the plastic darts and dartboard, which will serve as persistent physical reminders of your motif and memorable message.

Most Web developers will be familiar with MySQL, as it comes with most Web hosting packages and servers. Therefore, MySQL is the most commonly used database engine on the Internet. It s also the default engine used by the Ruby on Rails framework (to be covered in 13), so it s likely you ll be using it at some point. PostgreSQL and Oracle also have their own niches, with Oracle being a well-known enterprise-level database that can cost quite a lot of money to license. However, it s used by a lot of larger companies. For our purposes in the next few sections of this chapter, we ll be using a system called SQLite. Unlike MySQL, PostgreSQL, and Oracle, SQLite doesn t run as a server, so it doesn t require any special resources. Whereas MySQL, PostgreSQL, and Oracle all run as permanent server applications, SQLite is on-demand and works entirely on your local machine. Despite this, it s still fast and reliable, and is ideal for local database purposes. You can easily carry much of the knowledge you learn with SQLite across to other systems.

Nonetheless, toward the end of this chapter we ll look at how you can connect to databases using these other architectures, so that you can get direct access to your existing databases from your Ruby applications.

Returns the absolute value of a number Square root, also for negative numbers Converts a string or number to a floating-point number Offers interactive help Gets input from the user Converts a string or number to an integer Converts a string or number to a long integer Returns the ceiling of a number as a float Returns the floor of a number as a float Square root, not for negative numbers x to the power of y (modulo z) Gets input from the user, as a string Returns a string-representation of a value Rounds a number to a given precision Converts a value to a string

9

One of the major disadvantages of Ruby threads not being true operating system level threads is that if a thread needs to do something that calls the operating system and waits for a response, the entire Ruby threading scheduler is paused. However, for general operations Ruby s threading system is fine.

Here s a basic demonstration of Ruby threading in action:

threads = [] 10.times do thread = Thread.new do 10.times { |i| print i; $stdout.flush; sleep rand(2) } end threads << thread end threads.each { |thread| thread.join }