System Landscape 
The portal system landscape is a collection of systems. A system is a portal object comprised of a set of properties that represent an external, or back-end, application or Web service. Systems enable a connection to these applications and the retrieval of data from their information stores.
Caution
In SAP NetWeaver Composition Environment, use the portal system landscape or portal APIs for back-end connectivity to BI composite and SAP transaction iViews only. Use Remote Function Calls (RFCs) and Web services, configured in the SAP NetWeaver Administrator (NWA), to enable back-end connectivity for other applications types, such as composite views and guided procedures.
Integration
System information, including connectivity properties to back-end applications, and authorization information, if required, is contained in system templates in the PCD (Portal Content Directory).
You can create a new system based on existing system templates. It is also possible to generate a system template by executing an XML script, containing the system properties, and uploading it to the portal using the XML Content and Actions tool.
Information: XML Content and Actions
Some external applications to which you want to connect must have a connector deployed on the Web server of the portal. The connector is the middleware through which the portal content accesses the application.
The portal provides three connectors with its initial content: an SAP connector for accessing SAP systems, and a JDBC connector for accessing generic databases, and a Web Service connector for accessing Web services. These three connectors are automatically installed to the Web application server during portal installation.
It is possible to see the system landscape of any portal in the System Landscape Overview iView.