1. Naming
CSCI 4780/6780

2. DHT-based Approaches
Lookup functionality distributed among multiple nodes
Chord – m-bit identifier space (IDs range from 0 to 2m-1)
Lookup information on k will be maintained by succ(k)
Simple implementation: Node q keeps track of succ(q+1)
Finger table for scalable look up
q keeps track of succ(q+2i-1) for 0 < i < m

3. Distributed Hash Table

4. Hierarchical Approaches
Hierarchy of domains
Leaf domain – lowest level of the hierarchy
Location record for each entity
Leaf domain node stores the actual location of the entity
Upper level nodes store references to the children that contain the entity
Multiple addresses if entity is replicated

5. Hierarchical Location Service

6. Location Service for Replicated Entities

7. Lookup in Hierarchical Location Service

8. Insertion in Hierarchical Lookup Service

9. Insertion (Contd.)

10. Structured Naming Names are organized into name spaces
Name space is represented as a directed graph with two types of nodes
Leaf Node – Represents named entity
No outgoing edges
Stores information on the entity it is referring (address or state of the entity)
Directory node – Can have multiple outgoing edges each with a name
Directory table – Contains <edge label, node ID> for each outgoing edge

11. A general naming graph with a single root node.
Name Spaces - Example
A general naming graph with a single root node.

12. More on Name Spaces
Path name: Sequence of edge labels leading from one node to another
N:<label-1, label-2 …., label-n>
Absolute path name
First node is the root
Relative path name
First node can be arbitrary node
Global name
Denotes same entity where ever it is used
Local name
Interpretation is dependent upon where it is used

13. Organizing Name Spaces
Tree-based approach
Strict hierarchical approach
Directed acyclic graph
Most commonly used
General graphs
Rarely used
Single root
Multiple root

14. Name Spaces in Unix File System
The general organization of the UNIX file system implementation on a logical disk of contiguous disk blocks.

15. Name Resolution Process of looking-up an entity given its path name
Find the corresponding node
Example: N:<label-1, label-2 …. Label-n>
Start at N
Proceed along the edges
A crucial question: Where should the resolution begin?
Which node represents the root?
Unix example: Which i-node corresponds to the root?

16. Closure Mechanism
Knowing how and where to start resolution mechanism – Closure
Have a universally agreed upon root
In Unix root directory is the first i-node
Actual byte offset is calculated by other values in superblock
HOME variable in Unix – always refers to the user’s home directory