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Data Structures Using Java by Duncan A. Buell

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10 CHAPTER 1INTRODUCTION
1.2.2 Student Records
A classic kind of record to be stored and manipulated are the student records at
educational institutions. Each record contains several different kinds of data. Name,
student ID number, and such are going to be almost static. Address information,
major, and such will need to be updatable, but this together with the identity
information will be data “local to the student.” This will differ from the transcript
information. Both for privacy and efficiency reasons some information is likely to
be stored in different files from the address information. We would also not expect
the individual course grades to be stored with the student information; rather, we
would expect all the grade information for a given course to be stored in one place,
with the student record indexing into the course data.
In the case of student records, then, we have the likelihood that, unlike the card
catalog information for a document in a library, “the record” for a given student will
not consist of a single record, in a single array, in a single Java class (assuming Java
to be the implementation language). Indeed, in most significant implementations, a
single “record” is likely to be the aggregation of fields from several different stored
collections. One reason for this is to prevent duplication of data because duplication
leads to the problem of consistency across instances. If one list of grades by class
were kept and a separate list of grades by student existed, then changes would
have to occur in more than one location. This is always something to be avoided in
designing software.
1.2.3 Retail Transactions
A number of standard data processing environments constitute transaction process-
ing. For example, both a large retailer, such as Walmart, and a credit card processor,
such as Visa, deal with millions of individual transaction records every day that
come in on a pretty much nonstop basis. Characteristics of the data records will
be that they are small, with several fixed fields (date, payment method, purchase
location, and such), and a variable number of individual item purchases made. The
data records need to cataloged and stored, with multiple indexing and retrieval
patterns made possible, but it is unlikely that the individual items will be accessed
randomly or very often.
1.2.4 Packet Traffic
Internet packets resemble transaction records in many ways. One characteristic
of Internet packets is that they are more or less fixed size (a primary reason for
packetizing an Internet transmission is to keep the packet size small) and have
a number of fixed fields (source, destination, etc.). One characteristic somewhat

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