Database Reference
In-Depth Information
Both users and database administrators need all of the knowledge in this text. However,
the emphasis on each topic differs for the two groups. Figure 1-24 shows our opinion as to the
relative importance of each topic to each group. Discuss this table with your instructor. He or
she may have knowledge about your local job market that affects the relative importance of
these topics.
Database processing emerged around 1970 and has been continuously evolving and changing
since then. This continual change has made it a fascinating and thoroughly enjoyable field in
which to work. Figure 1-25 summarizes the major eras of database processing.
The early years
Prior to 1970, all data were stored in separate files, most of which were kept on reels of mag-
netic tape. Magnetic disks and drums (magnetic cylinders that are no longer used) were
exceedingly expensive and very small. Today's 1.44-megabyte floppy disk (which is now itself
a limited-use technology) has more capacity than many disks of that era. Memory was expen-
sive as well. In 1969, we were processing payroll on a computer that had just 32,000
bytes
of
memory, while the computer on which this history is being written has 8
gigabytes
of m emor y.
Integrated processing was an important but very difficult problem. An insurance com-
pany, for example, wanted to relate customer account data to customer claim data. Accounts
were stored on one magnetic tape, and claims were stored on another. To process claims, the
data on the two tapes had to be integrated somehow.
The need for data integration drove the development of the first database technology.
By 1973, several commercial DBMS products had emerged. These products were in use by
the mid-1970s. The first edition of this text, copyrighted 1977, featured the DBMS products
ADABAS, System2000, Total, IDMS, and IMS. Of those five, only ADABAS and IMS are still in
use, and neither of them has substantial market share today.
Those early DBMS products varied in the way that they structured data relationships. One
method, called
Data Language/I (DL/I)
used hierarchies or trees (see Appendix G) to repre-
sent relationships. IMS, which was developed and licensed by IBM, was based on this model.
IMS had success at many organizations, particularly among large manufacturers, and is still in
limited use today.
Figure 1-24
Priorities of What
You Need to Know
Topic
Chapter
Importance to Knowledge
Worker and Programmer
Importance to Database
Administrator
Basic SQL
Chapter 2
1
1
Design via normalization
Chapter 3
2
1
Data modeling
Chapter 4
1
1
Data model transformation
Chapter 5
2
1
DDL SQL
Chapter 6
2
1
Constraint enforcement
Chapter 7
3
1
Database redesign
Chapter 8
3
2, but 1 for senior DBA
Database administration
Chapter 9
2
1
SQL Server, Oracle,
MySQL specifics
Chapters 10, 10A, 10B, 10C
3
1
Database application technology
Chapters 11, 12
1
3
1 = Very important; 2 = Important; 3 = Less important
Warning: Opinions vary, ask your instructor for his or hers.
Search WWH ::
Custom Search