Uniform resource locator. A standard for writing a textual reference to an arbitrary piece of data in the World Wide Web. A URL looks like this: protocol://host/localinfo where protocol specifies a protocol for fetching the object (such as http or ftp), host specifies the Internet name of the targeted host, and localinfo is a string (often a file name) passed to the protocol handler on the remote host.

Here are three basic types of runtime errors in PHP:
1. Notices: These are trivial, non-critical errors that PHP encounters while executing a script - for example, accessing a variable that has not yet been defined. By default, such errors are not displayed to the user at all - although you can change this default behavior.
2. Warnings: These are more serious errors - for example, attempting to include() a file which does not exist. By default, these errors are displayed to the user, but they do not result in script termination.
3. Fatal errors: These are critical errors - for example, instantiating an object of a non-existent class, or calling a non-existent function. These errors cause the immediate termination of the script, and PHP's default behavior is to display them to the user when they take place.

Web services allow access to software through standard web protocols such as HTTP and SMTP. They enable software to interact with a wider range of clients. Web services can be consumed by any application that understands how to parse an XML. XML is the key technology used in web services. Microsoft .net web services support three protocols HTTP GET, HTTP POST and SOAP (Simple Object Access Protocol). For the clients to interact with the web services there must be a description of the method calls or interface that the web service supports. This web service description document is found in the XML schema called as WSDL (Web services description language). Any WSDL capable SOAP client can use the WSDL file to get a description of the web service and invoke methods on the service.

Error handling that evolve around the various On Error.. statements are referred to as unstructured error handling. The build in object Err is used in this type of error handling. This object has several properties and methods as listed below: Properties:  Description: a short description of the error HelpContext: context ID for the help topic associated with the error HelpFile: fully qualified file name if any Number: Number associated with the error Source: a string that specifies the object that generated the error. Method: Clear: Clears the set values of all properties of the error object. Raise: Generates a runtime error and sets the properties of the Err object to the values supplied in the method call