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Naming II

Naming II. CSE 5306 Lecture Quiz 13 Due at 5 PM Tuesday, 23 September 2014. 5.3 Structured Naming. Flat names work very well for computers. Simple, structured names are much more human readable. Computers accommodate our weaknesses in naming our files and Internet hosts.

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Naming II

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  1. Naming II CSE 5306 Lecture Quiz 13 Due at 5 PM Tuesday, 23 September 2014

  2. 5.3 Structured Naming • Flat names work very well for computers. • Simple, structured names are much more human readable. • Computers accommodate our weaknesses in naming our files and Internet hosts. • How are human-readable structured names resolved to computer-language addresses…?

  3. 5.3.1 Name Spaces • We organize names (and their addresses) into name spaces. • Labeled, directed acyclic graph name spaces have (pointer) directory nodes and (address bearing) leaf nodes(figure 5-9 above). • A directory node contains a directory table that identifies its outgoing paths (i.e., the directed edges above). • There can be one or more root (directory) nodes. • A leaf node also can be the named file itself, the state of that file, etc. • A sequence of paths is called a path name. • If a path’s first node is the root, the path is called an absolute path name. If it is not the root, the path is called a relative path. • A local name refers to various entities in many contexts, but a global name refers to just one entity wherever it may appear. • All resources can be named with strings; e.g., /home/steen/keysor /keys.

  4. 5.3.1 Name Spaces (continued) • UNIX’ file system addresses a contiguous series of logical disk blocks (Figure 5-10 above). • The initial boot block contains instructions for loading the operating system into main memory. • The super block stores the file system’s size, a list of directory node (inode) addresses, and a list of unused disk blocks.

  5. 5.3.2 Name Resolution • Looking up information in a name space node, which is identified by a given name, is called name resolution. • We recursively traverse the directory tree from top to bottom, by reading the sequence of edge names in the path and looking them up in inode directory tables. • Finally we read the information in the leaf node.

  6. R U O K ? Match the following terms with their definitions below. • Name space __ • Directed acyclic graph __ • Directory nodes __ • Leaf node __ • Path name__ • Absolute path __ • Relative path __ • Local name __ • Global name __ • A graph termination that contains an address, a named file or its state. • A path whose first node is the root. • Contains a table that identifies outgoing paths (directed edges). • A hierarchy of linked name pointers and address-bearing leaf nodes. • A sequence of graph edge names. • An organized list of entity names and their addresses. • Refers to various entities in many contexts. • A path whose first node is not the root. k. Refers to just one entity, wherever it may appear

  7. R U O K ? Match the following terms with their definitions below. 10. boot block __ 11. Super block __ 12.Inode__ 13. name resolution __ 14. closure mechanism __ a. Looking up information in a name space node, which is identified by the given name. b. Stores the file system’s size, a list of directory node addresses and a list of unused disk blocks. c. A directory node. d. The initial UNIX disk block that contains instructions for loading the operating system into main memory. e. The knowledge of how and where to begin the name resolution process.

  8. 5.3.2 Closure Mechanism • The knowledge of how and where to begin the name resolution process is called a closure mechanism. • UNIX’ closure mechanism calculates the disk address of the file system’s root node from address offsets in the disk’s superblock. • The plain old telephone system’s (POTS) closure mechanism tells its clients how to use the string “8172725555.” • UNIX’ HOME local name always refers to the user’s home directory, by virtue of a closure mechanism that resolves that name to a node in UNIX’ user directory.

  9. 5.3.2 Linking & Mounting • An alias is another name for the same entity; e.g., an environment variable. • Name spaces allow two kinds of aliasing: • Hard links; e.g., the multiple absolute paths /keys or /home/steen/keys on slide 3. • Symbolic links; i.e., a leaf node stores an absolute path to a directory, which conjoins the initial path. • A mount point is a directory node that stores an identifier of foreign name space’s (root) directory node, which is called a mounting point. • If the mount and mounting point are distributed to different machines, the initiating server needs to resolve: • The foreign server’s name to a Web URL or LAN address. • Its access name (e.g., nfs) to a communication protocol. • The mounting point’s name to one node ID in its name space. For example, a mobile laptop might use Sun’s Network File System (NFS) to download this file from the directory nfs://ranger.uta.edu/~morgan.

  10. 5.3.3 Implementing a Name Space • Large-scale distributed systems spread their (domain) name spaces over multiple hierarchical name servers (see Figure 5-13 above).

  11. 5.3.3 Name Space Distribution • The hierarchy’s global layer includes DNS’ root and many stable organization groups. • The administrational layer consists of nodes internally managed by named organizations. • The managerial layer has nodes that change regularly; e.g., LAN hosts, shared binary files. • Zonesare non-overlapping parts of DNS implemented by separate name servers, which fulfill different requirements (Fig. 5-14 above).

  12. 5.3.3 Implementing Name Resolution • A name resolver is responsible for ensuring that name resolution is carried out: • It hands root:<nl,vu,cs,ftp,pub,globe,index.html> (i.e., ftp://ftp.cs.vu.nl/pub/globe/index.html) to the root name server at a well known address, which returns only the nl name server’s address. • It hands nl:<vu, cs, ftp, pub, globe,index.html> to the nl name server, which returns only the vu name server’s address. • This iteration (Fig. 5-15, above left) continues till the resolver IDs <cs>. • The equivalent recursive process (Fig.5-16, right) requires lower-layer name servers to call upon each other till <cs> is identified: • They have time for such duties • Their proximity lowers communication costs. • Their caching of frequent name requests makes them more efficient.

  13. R U O K ? 15. Which of the following is NOT a good example of name resolution closure mechanisms? __ • UNIX calculates the disk address of the file system’s root node from address offsets in the disk’s superblock. • POTS tells its clients how to use the string “8172725555.” • The U.S. Senate votes to stop discussion on its Syrian Invasion resolution. • UNIX’ HOME local name always refers to the root of the user’s home directory, and UNIX resolves that name to a node in its /users/ directory.

  14. R U O K ? Match the following terms with their definitions below. 16. Alias __ 17. Hard link __ 18. Symbolic link __ 19. mount point __ 20. mountingpoint __ a. A directory node that stores the identifier of foreign name space’s (root) directory node. b. The absolute path /keys or /home/steen/keys on slide 3. c. A leaf node that stores an absolute path to a directory, which conjoins the initial path. d. A (root) directory node, which is pointed at by foreign name space. e. Another name for the same entity; e.g., an environment variable.

  15. R U O K ? 21. If a mount and its mounting point are distributed to different machines, what names must the initiating server resolve? __ • The foreign server’s name to a Web URL or LAN address. • Its access name (e.g., nfs) to a communication protocol. • The mounting point’s name to one node ID in its name space. • All of the above. • None of the above.

  16. R U O K ? Contrast DNS’ three layers by matching them with the traits below. 22. Geographic network scale is organizational. __ 23. Vast number of nodes. __ 24. Lookup latencies in the seconds. __ 25. Lazy update propagation. __ 26. No replicas. __ 27. Sometimes client-side caching is applied. __ • Global layer. • Administrational layer. • Managerial layer.

  17. R U O K ? Match the following terms with their definitions below. 28. Global layer __ 29. Administrational layer __ 30. Managerial layer __ 31. DNS zones __ 32. Name resolver __ 33. Iterative name resolution __ 34. Recursive name resolution __ • Nodes that change regularly; e.g., LAN hosts, shared binary files. • Lower-layer name servers call upon each other, till lowest level server is identified. • Nodes internally managed by named organizations. • Client calls upon name servers from highest to lowest, and each server identifies the next. • Responsible for ensuring that names are fully resolved. • Includes DNS’ root and many stable organization groups. • Non-overlapping parts implemented by separate name servers, which fulfill different requirements.

  18. R U O K ? 35. Which of the following is NOT an advantage of using managerial-level name servers to recursively resolve names? __ • They have time for such duties • Their proximity lowers communication costs. • Their caching of frequent name requests makes them more efficient. • They do not tend to be replicated.

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