Why Is the Expression Language Not SQL or Visual Basic?
Neither SQL nor Visual Basic meets the requirements of the DTS data flow. For example, we wanted to support a range of operators such as bitwise operators manipulating bitmasks that are used in many scenarios as flags. Also, in order to make best use of memory (and thus get the best performance) the DTS data flow is strict about data types–this is also reflected in the expression syntax. The DTS expression syntax enables you to design high-performance data flows with complex handling of strings and data types. If there are functions you need which are not supported by the expression language, or if you would prefer to use Visual Basic syntax, you can use the Script Component which enables you to work with Visual Basic .NET in the data flow.
