Fall, 2017
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Fall, 2017 |
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What is a Database??
There is a relatively simple definition of a database: "A database is a large, logical, integrated collection of data and metadata" ??? What
does that mean ??? Let's break down the statement:
Data. We discuss data below.
??? OK, You
said you would talk about data ???
Mary is an 'A' Student Tells us something about Mary (She is an 'A' Student). It expands our knowledge (about Mary). If we were to keep data (remember, this is plural) about Mary, we might store: Smith, Mary 34 92 123 MIS 778 INFOSYS
??? How else can we characterize databases ???
??? What is it really ??? It is how an organization stores information. The university, for example, keeps a lot of information about you (Your address, major, courses taken, grades received, an so forth). All of this data is stored in a database. ??? How is this data stored??? Consider the following statement:
Diagramatically, this could be stated as:
??? Why should we use databases ??? That is the next topic
This page was last updated on 02/26/04.
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We are all relatively familiar with databases, and we see
them everyday. As stated in the Course description, "Databases have become THE most important Information System package for
Corporations. Without them, most companies would have a hard time functioning. MOST (and
that truly means almost all) Companies could NOT exist without them."
Imagine what a corporation such as American Express, with approximately 30
Million customers, world wide, would do without them.
Large. We make the assumption that we
are dealing with a lot of data (by the way, data is the plural of datum (a
single piece of data)). We are assuming that we are dealing with a large number
of records (to be defined later), such as American Express. far too large a
number to be dealt with in Random Access Memory.
Logical. As users of the database, we
are not necessarily concerned with how the database is actually (physically)
stored. As we will see later, we have a logical view of the database, and are
able to access the data contained in it according to how we visualize it.
Integrated
Collection. We make the assumption
that we are inter-relating a number of different subject areas. For example, as
a student, there are different areas which are concerned with you: The registrar
is concerned about what courses you are taking; the bursar is concerned with how
much (if any) you owe them; the instructor of a course is concerned with how you
are doing in the class. All of these are separate issues, but are related by one
issue: You, the student. It is basically the difference between a
spreadsheet (such as Excel) and a database (such as Oracle or Access), A
spreadsheet is set-up for a specific purpose (the registrar, bursar, or
instructor might keep spreadsheets on you), whereas a database keeps
general information (data - we'll discuss the difference later) about
you which all of the areas can draw from.
Metadata. Metadata is data about data.
Which tells
us essentially nothing about Mary. However, looking at the data above, we do get the feeling
that there is a pattern as to how it is stored. That gives us a basic definition
for data: data is a non-random collection of symbols.
It
is a way of modeling the 'real-world' (at least parts of it). It refers to
entities (something
we wish to keep data on -- i.e., people places, things), entity
attributes (specific data
about an entity -- e.g., a person's height, a place's area code, a thing's
dimensions) and the relationships
between entities (e.g., an order may contain several parts).
