L1-Why DBS

Why DBS?
Questions to be answered when we learn any subject can be categoried as
Why ==> the purpose or main problem
What ==> steps in the solution
How ==> details
In this book, the why question is answered with Chapter 1, mostly by describing what DBS's can do. The
what questions are answered by each subsequent chapters. In each chapter, detailed descriptions of
how exactly DBS's functions are handled.
We will try to give a big picture of our course in this class. But let's start with the simple illustration that
we used last time showing DB, DBMS, and DB Apps.
[insert chart]
Practically, when a DB is used, a DBMS is used: so in this text, DBS is used to refer to both.
[definitions for DB and DBS from the text]
Till now, we haven't defined Data yet. Not even described it yet. In a short while, we will see the data
that need to be stored are far more complex than you might have thought.
In this text, as in some other DB texts, a simple DB about a college setting is used to show what data
need to be stored to support business processes of an institution.
[copy of five tables in the college DB, each with a few sample records]
Data in real world tends to be complex in nature. Even in this (overly) simplified sample DB, we see
different types of records, with each type representing a kind of people, entities, or processes in the
application domain. Furthermore, these records are interrelated, and often need to be used together in
answering business questions.
DB vs. (flat) files: or when to use (or not to use) a DB? (or What can a DBS do?)
According to your text, five requirements are fundamental for a DBS:
persistent: but both DB and files will do
large: and complex, may still manageable with flat files
shared: allow for multiple users to use the data concurrently, and for different purposes, and in
a timely manner
accuracy: keep the above requirements in mind, plus possible system failure
usable: sounds like a requirement for DB Apps at first. Soon we will see how to get a DBS
qualified for a usable one.
Who use it?
Before dig in deep about What functions DBS should provide, let's first exam who are going to use the
data, and in what different ways?
DBA: definition in your text
In-betweens: apps developers, report programmers, analysts, etc
Users (or end users, naive users):
What make DBS's usable?
Functions DBS's should provide (not a complete list)
record management
o user data
o relationship
o efficient access  index
multiple user access
o transaction control
o users and privileges
memory management
o DB cannot fit into memory  mapping between disk space and memory space
o Changes in memory need to be updated to disk
o Recovery
 Support for (application) development paradigm/principles
Data model  representing RealWorld with only features necessary [college DB as an example]
[definition from the text]
o DBA: physical data model, using file, disk
 how
o All but end users: conceptual (or logical), using tables, records, relationships  what
o End users: external, using application-specific terms, such as  what (or why)
 Students: transcripts
 Professors: rosters
 Deans: dean’s list, retention/graduation rate
Schema: [definition in the text]  instance of a model
o Schema: structure of a DB, static
o Instance: a snapshot of a DB, dynamic
Three-level architecture
o Physical data independence
o Logical data independence
The Big Picture  put it all together