Vertical Applications are specifically made for one domain.
Examples: Siebel ePharma , Siebel eFinance
Horizontal Applications are Common which can be used for any domain.
Examples: Siebel Call Center, Siebel Sales
Lets discuss this in detail

 Background
During normal Siebel application operations, transaction gaps are created in the Siebel Remote transaction queue. If the gap lasts longer than the wait period, the transaction represented by the gap will be skipped over and transactions will not be routed to respective mobile clients on the application server. This technical note discusses transaction gaps, their causes, and recommendations on how to minimize impact on a Siebel Remote deployment.
Summary
The following topics are discussed in this document:
            • What is a Transaction Gap?
            • How are Transaction Gaps Created?
            • …

Symptom or Error Message
The Transaction Router Siebel Remote server task may fail under certain conditions which will cause a backlog in the transactions to be routed to Siebel Remote mobile users and regional nodes. Symptoms of a Transaction Router failure are usually an error on the Status field on the Server task applet, and the Task State field would report that the task has exited with an error:
Task State: Exited with error
Status: ERROR: 1 client(s) failed with errors, 0 client(s) successful
To generate more detailed trace information:
            • In Siebel …

Learn about various types of tables used in siebel application.
• Repository Tables • Data Tables
• Base Tables • Interface Tables
• Extension Tables • XM Tables

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