11. What is a queue?
Ans: A queue is an ordered collection of items from which items may be deleted at one end (front end) and items inserted at the other end (rear end).
It obeys FIFO rule there is no limit to the number of elements a queue contains.

12. What is a priority queue?
Ans: The priority queue is a data structure in which the intrinsic ordering of the elements (numeric or alphabetic)
Determines the result of its basic operation. It is of two types
i) Ascending priority queue- Here smallest item can be removed (insertion is arbitrary)
ii) Descending priority queue- Here largest item can be removed (insertion is arbitrary)

13. What are the disadvantages of sequential storage?
Ans:
i) Fixed amount of storage remains allocated to the data structure even if it contains less element.
ii) No more than fixed amount of storage is allocated causing overflow

14. What are the disadvantages of representing a stack or queue by a linked list?
Ans:
i) A node in a linked list (info and next field) occupies more storage than a corresponding element in an array.
ii) Additional time spent in managing the available list.

15. What is dangling pointer and how to avoid it?
Ans: After a call to free(p) makes a subsequent reference to *p illegal, i.e. though the storage top is freed but the value of p(address) remain unchanged .so the object at that address may be used as the value of *p (i.e. there is no way to detect the illegality).Here p is called dangling pointer.
To avoid this it is better to set up to NULL after executing free (p).The null pointer value doesn’t reference a storage location it is a pointer that doesn’t point to anything.

16. What are the disadvantages of linear list?
Ans:
i) We cannot reach any of the nodes that precede node (p)
ii) If a list is traversed, the external pointer to the list must be persevered in order to reference the list again

17. In RDBMS, what is the efficient data structure used in the internal storage representation?
Ans: B+ tree. Because in B+ tree, all the data is stored only in leaf nodes, that makes searching easier. This corresponds to the records that shall
be stored in leaf nodes.

18. What do you mean by free pool?
Ans: Pool is a list consisting of unused memory cells which has its own pointer.

19. Define circular list?
Ans: In linear list the next field of the last node contain a null pointer, when a next field in the last node contain a pointer back to the first node it is called circular list.
Advantages – From any point in the list it is possible to reach at any other point

20. What do you mean by overflow and underflow?
Ans: When new data is to be inserted into the data structure but there is no available space i.e. free storage list is empty this situation is called overflow.
When we want to delete data from a data structure that is empty this situation is called underflow.