DATABASE SYSTEMS (phần 16) pps
DATABASE SYSTEMS (phần 16) pps
... followed
and
undone.
19.6
RECOVERY
IN
MULTIDATABASE
SYSTEMS
So far, we
have
implicitly assumed
that
a transaction accesses a single database. In some
cases
a single transaction, called a
multidatabase
transaction,
may ... Do
Not
Affect
the Database
In general, a transaction will
have
actions
that
do not affect
the
database, such as generat-
ing
and
printing
messages or reports from info...
DATABASE SYSTEMS (phần 9) pps
... a relational database schema for this database application. First show all
the
functional dependencies
that
should hold among
the
attributes.
Then
design
relation schemas for
the
database
that
are
each
in ... becomes
questionable
when
the
constraints
on
which
they
are based are hard
to
understand or to
detect
by
the
database designers
and
users
who
must discover these constraints. Thu...
DATABASE SYSTEMS (phần 12) pps
... block accesses to find a
specific
record in a file
with
b blocks.
Ordered
files are rarely used in database
applications
unless an
additional
access
path,
called a
primary
index,
is used; this results ... field.
Such
an organization is called
an
indexed
sequential
file
and
was used in a large
number
of early
IBM
systems. Insertion
is
handled
by some form of overflow file
that
is merged per...
DATABASE SYSTEMS (phần 15) pps
... it
contains
several
transaction
boundaries.
If
the
database
operations
in a
transaction
do
not
update
the
database
but
onlyretrieve data,
the
transaction
is called a
read-only
transaction.
The
model of a database
that
is used ... completes
execution
without error
or it fails
and
leaves
the
database unchanged.
554
IChapter 17
Introduction
to Transaction Processing Concepts and Theory...
DATABASE SYSTEMS (phần 1) ppt
... using,
and
imple-
menting
database
systems
and
applications.
Our
presentations
stresses
the
fundamentals
of database
modeling
and
design,
the
languages
and
facilities
provided
by
the
database
management
systems,
and
system
implementation
techniques.
The
book
is
meant
to
be
used ... I
Chapter
1
Databases
and
Database
Users
DATABASE
SYSTEM
UserS/Programmers
~
Application Programs/...
DATABASE SYSTEMS (phần 2) doc
... are
becoming
quite
popular.
These
systems provide an
environment for
developing
database
applications
and
include
facilities
that
help
in
many facets of
database
systems,
including
database
design,
CUI
development,
querying
and ... processing
and
optimization,
their
performance
improved. Eventually,
relational
databases
became
the
dominant
type of
database
systems
for traditiona...
DATABASE SYSTEMS (phần 4) pot
... additional facts from the
facts stored in a database.
Hence,
whereas most
current
database systems are limited
to answering direct queries, knowledge-based systems using
KR schemes
can
answer
queries
that
involve
inferences
over
the
stored ... relational database
and
a rela-
tional database schema. A
relational
database
schema
S is a set of relation schemas S =
(R
I
,
R
z
,
,...
DATABASE SYSTEMS (phần 5) ppt
... as
RM/T.
Childs
(1968)
had
earlier used set theory to model databases. Later,
Codd (1990) published a
book
examining over
300
features of
the
relational
data
model
and database systems.
Since Codd's pioneering ... discuss
JOIN
and
other
complex
binary
operations,
which
operate
on
two tables.
The
COMPANY
relational
database
shown
in
Figure 5.6 is used for
our
examples.
Some
common...
DATABASE SYSTEMS (phần 6) docx
... success
of
rela-
tional
databases in
the
commercial world. Because it became a standard for relational
databases,
users were less
concerned
about
migrating
their
database applications from
other
types of database
systems- for
example,
network
or ... 10
b
5
FIGURE
6.13
A
database
state for
the
relations T1
and
T2.
Relational Database
Design by
ER-
and
EER-to-Relational
Mapping
We now...
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