This is called a key attribute!
There are different types of key attributes!
Primary key is the key that is actually chosen, for example a social security number.
There is also a unique key, say our finger prints! they also uniquely identify humans, but usually we prefer to use social security number when we list people (a unique key could be a primary key if we chose so)
We could also identify people by their social security number and a name, but this is unnecessary, as social security number already gives a full identification. Such a reduntant key is called super key.
Answer:
1. tablets are less portable than smartphones
2. smartphones are considered necessities and tablets are considered luxuries
3. smartphones are personal devices; tablets are usually shared
4. Tablets have larger screens for more extensive use of applications as opposed to the smaller, less versatile mobile phone screens.
Firewalls are connected with a network device which blocks untrusted network forming a barrier in between trusted and un-trusted network.
