Validity Reliability Issues

"Research for its own sake." Is it really for its own sake? Why? How? How not? These questions are closely related to the well-known twin brothers in the area of research? Validity & reliability. These highly debated terms should be clarified at first stage: Lets me jot down the definitions from the book "Case Study Research" Lin (2003). Kidder and Judd defines the terms as below (as cited in Lin, 2003, p. 34). Other, additional definitions are also welcome.

Construct validity: Establishing correct operational measures for the concepts being studied.
Internal validity: (For internal and casual studies only) establishing a casual relationships whereby certain conditions are shown to lead other conditions, as distinguished from the spurious relationships.
External validity: Establishing the domain to which a studies findings can be generalized.
Reliability: Demonstrating that the operations of a study, such as the data collection procedures, can be repeated with the same results

In fact validity and reliability are evaluated differently for qualitative and quantitative research. Although the idea behind the terms are similar, how they are perceived is changed depending on the type of research design. Therefore, to understand these issues, there is a need to read them from multiple sources. One is provided below.

A nice resource which compare and contrast the meanings of validity and reliability for both qualitative and quantitative research: http://www.nova.edu/ssss/QR/QR8-4/golafshani.pdf