By Todd Schraml
Back in the 1970s, the ANSI SPARC three-tiered model arose, foreshadowing a smooth intertwining of data and architectural design. The three tiers concept isolated the physical storage needs of data structures independent of business' perception of these structures. The three levels were comprised of schemas labeled external, conceptual, and internal, with each level describing the data in focus from varying perspectives. Full article.
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