ug_gloss.htm

db.* (pronounced dee-be star) is an advanced, high performance, small footprint embedded database fo

occurrence of type A, there are many related occurrences of type B
and, for each occurrence of type B, there are many related
occurrences of type A. In <b><i>db.*</i></b>, <i>many-to-many
relationships</i> can be implemented using two <i>one-to-many</i>
sets through a third, intermediate record type.</font></p>
<p><font size="2"><strong>Member of set<br></strong> See
<strong>Set</strong> .</font></p>
<p><font size="2"><strong>Member pointer<br></strong> Stores set
membership linkage information. There is one <i>member pointer</i>
stored with a record per set for which the record is a member. Each
one contains the <i>database addresses</i> of the owner record,
previous member in the set, and next member in the set.</font></p>
<p><font size="2"><strong>Navigation</strong><br>
The process of retrieving records from a database by moving through
various set occurrences.</font></p>
<p><font size="2"><strong>Network database model<br></strong> A
data representation in which the relationships are explicitly
defined and maintained through <i>sets</i>.</font></p>
<p><font size="2"><strong>Node</strong><br>
A component of a <i>B-tree</i>, consisting of a page of sorted keys
stored in a key file.</font></p>
<p><font size="2">One-to-many relationship<br>
A relationship between two record types, A and B, such that for
each occurrence of type A, there are many related occurrences of
type B and, for each occurrence of type B, there is only one
related occurrence of type A.</font></p>
<p><font size="2"><strong>Owner of set<br></strong> See
<strong>Set</strong> .</font></p>
<p><font size="2"><strong>Page</strong><br>
Files are blocked into contiguous fixed-length segments called
<i>pages</i>. A <i>page</i> is the unit of database I/O performed
in <b><i>db.*</i></b>.</font></p>
<p><font size="2"><strong>Path name<br></strong> The sequence of
directories in a hierarchical file system that must be traversed to
locate a particular file.</font></p>
<p><font size="2"><strong>Pointer</strong><br>
In a database, a <i>pointer</i> is data stored in a record
occurrence that provides the necessary information for locating
related record occurrences. In a C program, a pointer is a variable
that contains a memory address.</font></p>
<p><font size="2"><strong>Process</strong><br>
An independently executing task or program. An individual execution
of a <b><i>db.*</i></b> application program.</font></p>
<p><font size="2"><strong>Queue</strong><br>
A <i>first-in-first-out</i> waiting list. Lock requests for a
locked resource will be placed at the end of a <i>queue</i>. When
the locked resource becomes available, the first lock request on
the queue will be granted.</font></p>
<p><font size="2"><strong>Record occurrence<br></strong> One
individual instance in a database of a record of a particular type.
A database consists of many occurrences of many different <i>record
types</i>. For example, an employee record type may consist of the
fields name, employee_id, job_title, and pay. An employee record
occurrence could be "<b>name: Jones, Jim; employee_id: c87101,
job_title: engr, pay: 3400</b>".</font></p>
<p><font size="2"><strong>Record type<br></strong> A named
collection of related <i>fields</i> that are stored and accessed as
a unit. See also <b>Record occurrence</b>.</font></p>
<p><font size="2"><strong>Record</strong><br>
Used synonymously with <i>record type</i> or <i>record
occurrence</i> depending on the context in which the term is
used.</font></p>
<p><font size="2"><strong>Recovery</strong><br>
The process of completing the <i>transaction</i> of a process that
failed during a <i>commit</i>.</font></p>
<p><font size="2"><strong>Redundant data<br></strong> Identical
data that is stored in multiple locations in a database. Typically
used to form relationships between tables in a relational database
management system.</font></p>
<p><font size="2"><strong>Relational database model<br></strong> A
data representation in which a database is viewed as consisting of
two-dimensional tables, each composed of one or more columns.
Inter-table relationships are defined through use of common column
names and data. Tables and columns are analogous to
<b><i>db.*</i></b> records and fields, respectively.</font></p>
<p><font size="2"><strong>Root node<br></strong> The top or start
node of a <i>B-tree</i>.</font></p>
<p><font size="2"><strong>Runtime system<br></strong> The
<b><i>db.*</i></b> C language library functions that perform all of
the database access required by an application program while it is
executing.</font></p>
<p><font size="2"><strong>Schema</strong><br>
A conceptual model of the structure of a database that defines the
data contents and relationships. A <i>database definition
language</i> specification is an implementation of a particular
<i>schema</i>.</font></p>
<p><font size="2"><strong>Semaphore</strong><br>
An interprocess synchronization mechanism typically used to inform
processes of the occurrence of a particular event. It is used in
the UNIX version of <b><i>db.*</i></b> to inform the lock manager
of an abnormal process termination.</font></p>
<p><font size="2"><strong>Set</strong><br>
Specifies a <i>one-to-many</i> relationship between record types.
One occurrence of the <i>owner</i> record type is related to many
occurrences of a <i>member</i> record type. Also called a <i>set
type</i>.</font></p>
<p><font size="2"><strong>Set occurrence<br></strong> An individual
instance of a <i>set</i> in which one <i>owner</i> record
occurrence has one or more <i>member</i> record occurrences
connected to it.</font></p>
<p><font size="2"><strong>Set pointer<br></strong> Stores set
ownership linkage information. There is one <i>set pointer</i>
stored with a record per set for which the record is an owner. Each
one contains a count of the number of members in the set, the
<i>database address</i> of the first member record occurrence, and
the <i>database address</i> of the last member record occurrence in
the set.</font></p>
<p><font size="2"><strong>Set scan<br></strong> The process of
performing an ordered traversal through all (or a subset of all)
member record occurrences of a given <i>set
occurrence</i>.</font></p>
<p><font size="2"><strong>Slot</strong><br>
A position in a data or key file for storage of a single record or
key occurrence.</font></p>
<p><font size="2"><strong>Static record<br></strong> A <i>record
type</i> containing only data that seldom, if ever,
changes.</font></p>
<p><font size="2"><font size="2">Synchronization<br></font> The
process of ensuring that, in a multi-user database environment,
updates to shared data are performed serially, one user at a
time.</font></p>
<p><font size="2"><strong>System record<br></strong> A special
record type used to define the "top" record in a network database.
There is only one occurrence of the system record. It allows the
definition of a set owned by system so that access to records
through set relationships can be achieved.</font></p>
<p><font size="2"><strong>Timeout</strong><br>
An event that occurs when a lock request has waited on a queue
longer than a pre-determined amount of time. It is used to avoid
<i>deadlock</i>.</font></p>
<p><font size="2"><strong>Timestamping</strong><br>
A multi-user database technique that allows a process to detect
deletions and updates made by other processes.</font></p>
<p><font size="2"><strong>Transaction activity file<br></strong> A
database family-wide <b><i>db.*</i></b> file that stores the names
of all log files currently involved in a transaction <i>commit</i>.
It provides for automatic recovery in the event the lock manager
fails, or for one-user configurations.</font></p>
<p><font size="2"><strong>Transaction</strong><br>
A group of related database changes that are written to the
database as a single unit during a <i>commit</i>. The logical
consistency of a database is maintained by placing all related
updates within transactions.</font></p>
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