Writing a document consists of expressing information in words, pictures, etc. that describe the subject matter. Designing a lens consists of expressing information in numbers, words, drawings, etc. that describe the lens. The essence of both is the creation of information that is expressed in language. A book isn't done until the information is expressed; a lens design isn't either. A word processor helps the author create his document; OSLO helps the optical designer create his lens. In the new metaphor, the lens is the document.

In the early days of lens design, the prescription gave the curvatures, thicknesses, and glasses, plus the aperture, field, and wavelengths, just enough information to trace rays through it. Now, an overall design contains a great deal more information, including tolerances, coating specifications, and manufacturing details such as polishing grades, bevels, and cosmetic requirements. Although OSLO does not yet deal with all these aspects of a design, its data structure is able to contain much more than the simple lens prescription.

To make best use of OSLO you should understand the basic nature of the data used and produced by the program. OSLO data can be divided into four major groups: surface data, operating conditions, preferences, and the Spreadsheet Buffer. A fifth group would include miscellaneous items such as command arguments, fixed defaults, and various temporary data used internally.