Pitney Bowes MapInfo Professional - Manual (Page 184)

area that is the initial map display. If the live access table is being added as a layer to an existing Map
window, the layer will be fit to that Map window.
MapInfo Professional stores information about a live access table in a TAB file. This information is known
as metadata. MapInfo Professional uses metadata to store information about the live access table that
is needed to manage transactions between MapInfo Professional and the server database. Two of the
most important kinds of information stored in the metadata include the connection string and the query
you build from the DBMS Table Wizard, or Expert dialog box.
About Linked Tables
A linked table is a MapInfo Professional table that is a replica of a table downloaded from a remote
database and retains links to its remote database table. (The remote database table is known as a DBMS
table.) When MapInfo Professional downloads a table, it copies the entire contents of the table to the
local machine. Any changes you make to the copy can be committed to the server table at any time.
Linked tables can be used stand-alone or remain linked to the original server database. You can refresh
linked tables to rerun queries on a regular basis using the Refresh tool or from the Table >
Maintenance > Refresh DBMS Table menu. After editing data in a linked table, MapInfo Professional
saves it to the RDBS in a manner that resolves any multi-editing conflicts. Saving the edits made to a
linked table commits them to the server database as well as to the linked table.
Comparing and Contrasting Live and Linked Access to a Table
Use the following information to decide whether to work with your remote data tables live or linked.
Live Table Linked Table
Data is read from the DBMS Server as
required. When the data is locally cached, A full replica of the DBMS table is
downloaded to the client machine. The Definition
the life of the cache is limited to the current
session. local replica retains reference to the
remote data source (ODBC/OCI
Connection parameters); The downloaded
copy is retained across sessions of
MapInfo Professional.
Live tables are suitable for reading and
editing dynamically changing data; or data Linked tables are suitable for backdrop
display data, or data that does not change Suitability
sets that do not fit within the limits of 2 GB much. Linked tables are editable, as long
per data file. Live tables are recommended as the base tables they are based on are
editable.
if you want to maintain data security (the
data must remain only in a single secure
location).
The cost of data transfer is incurred a little
bit at a time. Live tables are accessed real As the data is entirely local, there is a
one-time cost of downloading the data, Performance
Factors
time from the database, as required. but subsequent access is fast, comparable
Optionally, records from the live table can to native table access, since the user does
be locally cached for the length of the not incur the cost of network traffic every
MapInfo Professional session. Caching time the data needs to be accessed for
mapping, or for analysis.
enhances performance, because the data
is not fetched multiple times as the user,
zooms, pans, or browses around the data.
This is a network intensive option. Linked tables are limited to 2 GB per data
file; Linked tables are not refreshed unless Limitations
the user explicitly refreshes the table. You
cannot pack a linked table. You cannot
modify the table structure of a linked table.
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Deciding to work with Linked or Live Access Tables