Booleans: Booleans can hold one of two values: true or false.

Integers: Integers hold whole numbers that can be either negative or positive (e.g. -39013, 23191). They do not hold numbers with a decimal or fraction.

Doubles: These serve as the compliment to integers for expressing numbers. Fractions can be expressed as doubles as well as irrational numbers (e.g. 3.14, 3.0000001).

Strings: Finally, these are a catch-all for scalars. Strings are any collection of letters and numbers that cannot be expressed by the previously mentioned types. The previous types can also be converted to strings, but you lose any operations (e.g. addition, subtraction) that could have otherwise been applied. Examples include "Hello", "Testing 12345", or even "21".

Arrays: Arrays are the most common type of vectors. They contain multiple values are each element of the array is indexed by a number (also called the "key"), 0 - (N-1) where N is the number of elements in the array. In some languages, arrays can contain mixed data types, that is to say that we could have an array with the values {12, "Hello world!", 3412.11} and they can even contain arrays of arrays (called multidimensional arrays).

Associative Arrays ("hashes"): Very similar to a normal array, except the 0 - (N-1) keys in the array are now replaced with strings. This is the most common form of returning multiple values from a SOAP call, e.g. Common_Module::get_disk_quota returns a hash with keys "used" and "total".

Objects: Just as strings are a catch-all for scalars, objects are a catch-all for vectors, although objects tend to be a bit more complex in certain circumstances. Objects are generally avoided in apnscp esprit and are only seen when created via a complexType in SOAP. At this time there are no instances of complexType and shouldn't be in the future.

Mixed: These are the true catch-all; mixed means that it can be anything. It can be a scalar or a vector. It could be a boolean or an object. Returned values &151; what a SOAP call sends back to your application — are never mixed, but parameters &151; things you pass off to a SOAP function, can be. This is done to simplify a function within the control panel, for instance we might have a function called File_Module::delete_files. It wouldn't be prudent to make 100 SOAP calls to remove 100 files in a directory. It would be more efficient to just make one call to File_Module::delete_files with an array of strings that represent the files to delete.