"piggyback...on..."
I am confused about one usage of "piggyback" as stated in verb 1.1 http://www.oxforddictionaries.com/definition/english/piggyback.
I will write my understanding of each example sentence below, on the right-hand side, please help me check it.

"1.1 Link to or take advantage of (an existing system or body of work)"

e.g.1 they have piggybacked their own networks on to the system=they have linked their own network to the system
e.g.2 A SOF distribution system is required to piggyback existing distribution nodes only as needed...=It is required to have a SOF system to take advantage of existing distribution nodes (not sure what it means).
e.g.3 Instead, Austrian shares are increasingly being seen as a way for investors to piggyback the economic upswing across the EU's accession states.=take advantage of the upswing?
e.g.4 Instead, he said he intends to piggyback his intelligent computing network on mobile phone networks.=build...on mobile phone network?

How will you use it?

Thanks a lot!

Question

"piggyback...on..."
I am confused about one usage of "piggyback" as stated in verb 1.1 http://www.oxforddictionaries.com/definition/english/piggyback.
I will write my understanding of each example sentence below, on the right-hand side, please help me check it.

"1.1 Link to or take advantage of (an existing system or body of work)"

e.g.1 they have piggybacked their own networks on to the system=they have linked their own network to the system
e.g.2 A SOF distribution system is required to piggyback existing distribution nodes only as needed...=It is required to have a SOF system to take advantage of existing distribution nodes (not sure what it means).
e.g.3 Instead, Austrian shares are increasingly being seen as a way for investors to piggyback the economic upswing across the EU's accession states.=take advantage of the upswing?
e.g.4 Instead, he said he intends to piggyback his intelligent computing network on mobile phone networks.=build...on mobile phone network?

How will you use it?

Thanks a lot!

Answer

This term would probably not be used in ordinary conversation.  It is generally used in a technical sense, as shown by your examples.  It means to use an existing system, usually a system of signals or wires, to do something new.  
In your example 1, the speaker probably does not mean to say that "they" connected their own network to the system, but rather that they used the existing computers, wires, routers, and Wi-Fi signals when "they" created their own network.  Basically this would mean there are two networks which use the same wires; the original network and the new one which is "piggybacking" on the system.  
I'm not sure what SOF refers to in example 2.
In example 3, it's more like "spread" than "take advantage of".  The accession states have their own economic systems, and the economic upswing can spread across those systems, or "piggyback" on them.  Buying Austrian shares causes this to happen.
In example 4, again he is not building a new mobile phone network, but instead he uses the existing signals to spread or create his "intelligent computer network".

For a simpler example, lets say that you have a system of devices which sends oranges from one building to another.  Your friend asks you for an apple, and he works in the other building.  You decide to piggyback your apple to him using the system which normally sends oranges.  So instead of 3 oranges, the other building receives 3 oranges and 1 apple.  You used the system in a new way, something it wasn't originally intended to do.

Answer

In your examples, 'piggyback' is relatively formal. You won't typically hear or need it in everyday speech. English is my native language and yet this word still tends to sort of confuse me in the way it's used here. The only time I personally ever use 'piggyback' is to refer to riding on someone's back. :-)

Answer

Only sentence 1 is a natural use of "piggyback". The word refers to the way a child is carried on the back of an adult, so it's a way of attaching one thing to another in a way that helps or benefits the thing being attached.

Sentences 2-4 don't say what the subject is being attached *to*.