Lec5 - ECE151 Lecture 5 Chapter 4 Naming ECE151 Lecture 5 1 Naming Names identifiers and addresses Name resolution Name space implementation

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ECE151 – Lecture 5 1 ECE151 – Lecture 5 Chapter 4 Naming
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ECE151 – Lecture 5 2 Naming Names, identifiers, and addresses Name resolution Name space implementation Essence: Names are used to denote entities in a distributed system. To operate on an entity, we need to access it at an access point . Access points are entities that are named by means of an address . Note: A location-independent name for an entity E , is independent from the addresses of the access points offered by E .
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ECE151 – Lecture 5 3 Identifiers Pure name: A name that has no meaning at all; it is just a random string. Pure names can be used for comparison only. Identifier: A name having the following properties: P1 Each identifier refers to at most one entity P2 Each entity is referred to by at most one identifier P3 An identifier always refers to the same entity (prohibits reusing an identifier) Observation: An identifier need not necessarily be a pure name, i.e., it may have content. Question: Can the content of an identifier ever change?
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ECE151 – Lecture 5 4 Name Spaces Essence: a graph in which a leaf node represents a (named) entity. A directory node is an entity that refers to other nodes. A directory node contains a (directory) table of (edge label, node identifier) pairs.
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ECE151 – Lecture 5 5 Name Spaces Observation: We can easily store all kinds of attributes in a node, describing aspects of the entity the node represents: Type of the entity An identifier for that entity Address of the entity’s location Nicknames ... Observation: Directory nodes can also have attributes, besides just storing a directory table with (edge label, node identifier) pairs.
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ECE151 – Lecture 5 6 Name Resolution Problem: To resolve a name we need a directory node. How do we actually find that (initial) node? Closure mechanism: The mechanism to select the implicit context from which to start name resolution: www.cs.vu.nl: start at a DNS name server /home/steen/mbox: start at the local NFS file server (possible recursive search) 0031204447784: dial a phone number 130.37.24.8: IP address of the VU’s Web server Question: Why are closure mechanisms always implicit ? Observation: A closure mechanism may also determine how name resolution should proceed
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7 Name Linking Hard link: What we have described so far as a path name : a name that is resolved by following a specific path in a naming graph from one node to another. Soft link: Allow a node O to contain a name of another node: First resolve O ’s name (leading to O ) Read the content of O , yielding name . Name resolution continues with name . Observations: The name resolution process determines that we read the content of a node, in particular, the name in the other node that we need to go to. One way or the other, we know where and how to start
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This note was uploaded on 05/04/2008 for the course ECE 151 taught by Professor Melliar-smith during the Spring '08 term at UCSB.

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Lec5 - ECE151 Lecture 5 Chapter 4 Naming ECE151 Lecture 5 1 Naming Names identifiers and addresses Name resolution Name space implementation

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