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Part III. Appendix 2: Data Transport• Section 3.3.1 discusses services which contribute to the “thickness” of every IOOS Data Transportclient and server,• Section 3.3.2 considers services which could be implemented at selected servers.Universal minimal requests and facilitiesBy “universal minimal requests and facilities” we mean those requests that every IOOS Data Transportuser can make in every appropriate request to any IOOS Data Transport server with the fullexpectation that the request will be satisfied by that server without participation of an intermediateIOOS Data Transport server.On-line acquisition of data into legacy application packages from a varietyof data sourcesRequiring “on-line acquisition” is taken to mean having a Web-mediated transaction with brief,hopefully imperceptible, waiting time between requests and responses. Provision may be made fora “batch mode” where very large or very many data sets can be transmitted at times more convenientto client or server. This is a topic for further examination.Specifying “legacy applications” means modifying, wherever feasible, existing analysis and visualizationsoftware packages to participate as clients in the IOOS DT system. These packages are inmany instances expensive, familiar, capable, and customized: the investment they represent is considerableand “legacy” does not imply obsolescence. Fortunately, many such packages do providemechanisms for adding interfaces to new data sources, as will be required here. MATLAB is a primeexample of a legacy application.The “variety of data servers,” of course, means not simply that data are to be fetched from manysites. It also means that sites may store data as they see fit and yet will be able to fill requests forportions of that data submitted by any IOOS DT client site without prior arrangement.“Acquisition of data” is shorthand for what will be, for the IOOS DT system, at times a particularlyintricate process, principally because files at the servers will not be inviolate, atomic units ofdata transfer. Instead, IOOS DT clients will have to be able to ask a server to return just part of afile and, more than that, not simply a sequence of bytes between two positions in the file but projectionsand selections of the data. Specifics of such a request will have to be available to be communicatedby every client, and these same specifics will have to be intelligible to every IOOS DTserver, moreover. Benefits of the ability to tailor requests and responses so closely to the client’s154