1. Why Middleware Matters Arnold Rots Jonathan McDowell

2. Why Look under the Hood? The VO is intended to be user-friendly and we shouldn’t bother users with technical trivia It’s good to be aware that there needs to be something under the hood which requires resources For the more sophisticated user having some idea of what is under the hood helps in taking full advantage of the VO

3. Data Model If different client applications and different data repositories want to be able to communicate with each other, they need to have a common understanding of what it is they are talking about –A concept of the subject matter –Exchange sufficient information –Unambiguous (consistent) information –Use a common vocabulary

4. Metadata This means that (under the hood) there need to be explicit and precise standards on the metadata that are exchanged And an infrastructure of middleware tools to handle these

5. Space and Time Metadata Need to be explicit and precise –Near field / far field: Your galaxy cluster image may be of interest to solar system research: state where you were when you took the picture –Time: For precision timing it matters whether you use UTC or TT, and where your reference point is –Doppler velocities Just because you do, don’t assume everybody else defines Doppler velocity using LSR and radio def.

6. Spectral Energy Distributions SEDs are extremely important – and extremely tricky Try combining radio flux densities, IR & optical magnitudes, X-ray fluxes, Γ-ray photons into a coherent and consistent spectrum It requires specific knowledge in terms of metadata, conversions, and algorithms

7. We Need this Stuff The VO does not want to bore you with the ins and outs of what’s under the hood And you don’t need to know much about it But you do need to be aware that ease of use requires an infrastructure If it is crucial for you to know what can and cannot be done, the information is available