<sect1>
<title>Terminology</title>

<para>
In the following documentation,
<firstterm>site</firstterm>
may be interpreted as the host machine on which 
<Productname>Postgres</Productname> is installed.
Since it is possible to install more than one set of 
<Productname>Postgres</Productname>
databases on a single host, this term more precisely denotes any
particular set of installed 
<Productname>Postgres</Productname> binaries and databases.
</para>

<para>
The 
<Productname>Postgres</Productname> <firstterm>superuser</firstterm>
is the user named <replaceable>postgres</replaceable>
 who owns the <Productname>Postgres</Productname>
binaries and database files.  As the database superuser, all
protection mechanisms may be bypassed and any data accessed
arbitrarily.  
In addition, the <Productname>Postgres</Productname> superuser is allowed to execute
some support programs which are generally not available to all users.
Note that the <Productname>Postgres</Productname> superuser is
<emphasis>not</emphasis>
the same as the Unix superuser (which will be referred to as <firstterm>root</firstterm>).
The superuser should have a non-zero user identifier (<firstterm>UID</firstterm>)
for security reasons.
</para>

<para>
The
<firstterm>database administrator</firstterm>
or <acronym>DBA</acronym>, is the person who is responsible for installing 
<Productname>Postgres</Productname> with mechanisms to
enforce a security policy for a site.  The DBA can add new users by
the method described below 
and maintain a set of template databases for use by
<application>createdb</application>.
</para>

<para>
The <application>postmaster</application>
is the process that acts as a clearing-house for requests 
to the <Productname>Postgres</Productname> system.
Frontend applications connect to the <application>postmaster</application>,
which keeps tracks of any system errors and communication between the
backend processes.  The <application>postmaster</application>
can take several command-line arguments to tune its behavior.
However, supplying arguments is necessary only if you intend to run multiple
sites or a non-default site.
</para>

<para>
The <Productname>Postgres</Productname> backend
(the actual executable program <application>postgres</application>) may be executed
directly from the user shell by the 
<Productname>Postgres</Productname> super-user 
(with the database name as an argument).  However,
doing this bypasses the shared buffer pool and lock table associated
with a postmaster/site, therefore this is not recommended in a multiuser
site.
</para>
</sect1>

<sect1>
<title>Notation</title>

<para>
<quote>...</quote> or <filename>/usr/local/pgsql/</filename> 
at the front of a file name is used to represent the
path to the <Productname>Postgres</Productname> superuser's home directory.
</para>

<para>
In a command synopsis, brackets
(<quote>[</quote> and <quote>]</quote>) indicate an optional phrase or keyword.
Anything in braces
(<quote>{</quote> and <quote>}</quote>) and containing vertical bars (<quote>|</quote>)
 indicates that you must choose one.
</para>

<para>
In examples, parentheses (<quote>(</quote> and <quote>)</quote>) are used to group boolean
expressions.  <quote>|</quote> is the boolean operator OR.
</para>

<para>
Examples will show commands executed from various accounts and programs.
Commands executed from the root account will be preceeded with <quote>&gt;</quote>.
Commands executed from the <Productname>Postgres</Productname>
superuser account will be preceeded with <quote>%</quote>, while commands
executed from an unprivileged user's account will be preceeded with
<quote>$</quote>.
<acronym>SQL</acronym> commands will be preceeded with <quote>=&gt;</quote>
or will have no leading prompt, depending on the context.
</para>

<note>
<para>
At the time of writing (<Productname>Postgres</Productname> v6.4) the notation for
flagging commands is not universally consistant throughout the documentation set.
Please report problems to
<ulink url="mailto:docs@postgresql.org">the Documentation Mailing List</ulink>.
</para>
</note>

</sect1>
