Hi dear,

An SDI comprises the people, policies and technologies necessary to enable the generation and use of spatially referenced data through all levels of government, the private and non-profit sectors and academia. Following are few functions of SDIs:

• Data Publication and search
• metadata Catalog
• Testing of different data collection methods
• main    interfaces  to find     geospatial     resources.
• Outreach
• General administration

Good Luck

If you are asking about SDI in technology then here is your answer:

Serial Digital Interface ( SDI ) is a digital video interface that is used for the transmission of uncompressed, unencrypted digital video signals for professional video equipment. Standard SDI cables are terminated with BNC connectors and have a nominal impedance of 75 Ohms.

I would request you to provide the full forms in the question. This will reduce the miscommunication(if any).

I hope my answer helps. Have a great day!