Information Technology Reference
In-Depth Information
Is the two-phase commit a synchronous event? The parallel is often
drawn to the exchange of marriage vows where both must say “I do” for
the marriage to be finalized.
Hierarchical versus Structured
When one hears of a structured approach to solving a problem, one
immediately thinks of partitioning the problem into smaller tasks and then
working on each of them — the “divide and conquer” approach that has
served us so well in the past. The structure of something is its framework
that shows how its parts relate to each other, how it is “put together.”
When things are put together, sub-assemblies are created, physically
or logically. This raises the question: is all structured problem solving
hierarchical?
The answer is important because most people reach for a hierarchy
when they need to structure something. Hierarchies seem to be ingrained
in human thinking. Such hierarchies can be based on “superiority,” as in
the military where the upper levels of the hierarchy are considered
“superior” to the lower in many ways. They can be based on “contain-
ment,” where the upper levels comprise the lower ones, in different ways,
such as in geometry, where the class of polygons includes triangles
and quadrilaterals, which in turn could include isosceles and rectangle,
respectively.
Both can be visually represented as tree structures — classical node-
link diagrams that connect nodes together with line segments (Figure A.8)
— or diagrams that use indentation, sometimes called “bullet points”:
Polygons
Triangles
Isosceles
Quadrilaterals
Rhombus
Rectangle
Structure is also used to denote “order” in a set of things. Structure is
not necessarily limited to a hierarchy. Hierarchy is one of the options.
One could also have an enumerative approach to order lists of items, for
example, by value, date, weight, or size. The alphabets of the English
language are given a structure but do not work in a hierarchy.
Data structures were previously a popular term in systems design: “are
the data structures ready?” was a common question. The selection of the
appropriate data structure spelled the difference between efficient and
