Paper: What goes around comes around
- Physical and logical data independence are highly desirable
- Tree structured data models are very restrictive
- It is a challenge to provide sophisticated logical reorganizations of tree structured data
- A record-at-a-time user interface forces the programmer to do manual query optimization, and this is often hard.
- Networks are more flexible than hierarchies but more complex
- Loading and recovering networks is more complex than hierarchies
- Set-a-time languages are good, regardless of the data model, since they offer much improved physical data independence.
- Logical data independence is easier with a simple data model than with a complex one.
- Technical debates are usually settled by the elephants of the marketplace, and often for reasons that have little to do with the technology.
- Query optimizers can beat all but the best record-at-a-time DBMS application programmers.
The Entity-Relationship Era
- Functional dependencies are too difficult for mere mortals to understand. Another reason for KISS (Keep it simple stupid).
- Unless there is a big performance or functionality advantage, new constructs will go nowhere.
The Semantic Data Model Era (Similar to R++ Era)
- Packages will not sell to users unless they are in “major pain”
- Persistent languages will go nowhere without the support of the programming language community.
The Object-Relational Era
- The major benefits of OR is two-fold: putting code in the data base (and thereby blurring the distinction between code and data) and user-defined access methods.
- Widespread adoption of new technology requires either standards and/or an elephant pushing hard.
Semi Structured Data
- Schema-last is a probably a niche market
- XQuery is pretty much OR SQL with a different syntax
- XML will not solve the semantic heterogeneity either inside or outside the enterprise.