1 / 20

INF 123 SW Arch, dist sys & interop Lecture 10

INF 123 SW Arch, dist sys & interop Lecture 10. Prof. Crista Lopes. Objectives. Understanding of external data representations why well-known ones. Distributed System. No shared memory Different processors may represent data differently “ endianness ”: little endian , big endian. ….

shadow
Télécharger la présentation

INF 123 SW Arch, dist sys & interop Lecture 10

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. INF 123 SW Arch, dist sys & interopLecture 10 Prof. Crista Lopes

  2. Objectives • Understanding of external data representations • why • well-known ones

  3. Distributed System • No shared memory • Different processors may represent data differently • “endianness”: little endian, big endian … Component n Component n Component n Component1 Component1 Component1 Network Network OS Network OS Network OS Hardware Hardware Hardware Host 2 Host 1 Host 3

  4. Endianness • Big endian • Little endian

  5. Coping • IP defines a standard byte order (big endian) • Standard socket implementations provide converters • htonl, htons (host to network – 32 and 16 bits) • ntohl, htohs (network to host – 32 and 16 bits) • Problem solved by standardization at this level

  6. Binary vs. text data • Choice in protocol design: • number 132: 1000 0100 • text “132”: 0011 0001 0011 0011 0011 0010 • Tradeoff: compactness vs. readability • What would HTTP look like in binary??? • Many above-transport protocols choose latter

  7. Next: payload data struct Folder { UUID parentID; UUID owner; short type; short version; string name; UUID id; } ? too many options! obj host 1 host 2

  8. Well-known data representations • eXternal Data Representation – XDR (IETF 1995) • eXtensible Markup Language – XML (W3C 2008) • long history, back to 60’s • JavaScript Object Notation – JSON (IETF 2006)

  9. XDR • Binary data (i.e. hard to parse for humans) • Defines several basic data types • Does not include type information with data • receiver is assumed to know what types are being sent

  10. XDR example Data to be transmitted const MAXUSERNAME = 32; /* max length of a user name */ const MAXFILELEN = 65535; /* max length of a file */ const MAXNAMELEN = 255; /* max length of a file name */ /* * Types of files: */ enumfilekind { TEXT = 0, /* ascii data */ DATA = 1, /* raw data */ EXEC = 2 /* executable */ }; /* * File information, per kind of file: */ union filetypeswitch (filekind kind) { case TEXT: void; /* no extra information */ case DATA: string creator<MAXNAMELEN>; /* data creator / case EXEC: string interpretor<MAXNAMELEN>; /* interpreter */ }; /* * A complete file: */ structfile { /* name of file */ string filename<MAXNAMELEN>; /* info about file */ filetype type; /* owner of file */ string owner<MAXUSERNAME>; /* file data */ opaque data<MAXFILELEN>; };

  11. XDR example OFFSET HEX BYTES ASCII COMMENTS ------ --------- ----- -------- 0 00 00 00 09 .... -- length of filename = 9 4 73 69 6c 6c sill -- filename characters 8 79 70 72 6f ypro -- ... and more characters ... 12 67 00 00 00 g... -- ... and 3 zero-bytes of fill 16 00 00 00 02 .... -- filekind is EXEC = 2 20 00 00 00 04 .... -- length of interpretor = 4 24 6c 69 73 70 lisp -- interpretor characters 28 00 00 00 04 .... -- length of owner = 4 32 6a 6f 68 6e john -- owner characters 36 00 00 00 06 .... -- length of file data = 6 40 28 71 75 69 (qui -- file data bytes ... 44 74 29 00 00 t).. -- ... and 2 zero-bytes of fill

  12. XML • Textual data (i.e. humans can easily parse it) • User-defined data • No predefined types, just syntax • Includes type information with data • Receiver is assumed to know what types mean

  13. XML example <?xml version="1.0" encoding='UTF-8'?> <bookstore>   <book category="COOKING">    <title lang="en">Everyday Italian</title>    <author>Giada De Laurentiis</author>    <year>2005</year>    <price>30.00</price>  </book>   <book category="CHILDREN">    <title lang="en">Harry Potter</title>    <author>J K. Rowling</author>    <year>2005</year>    <price>29.99</price>  </book> </bookstore> XML Declaration Tag (start) Attribute Content Markup … … Tag (end) Element

  14. XML Namespaces (XMLNS) • Used to disambiguate tags • Not used by parser – info for humans go here and see what’s there <root> <h:tablexmlns:h="http://www.w3.org/TR/html4/"> <h:tr> <h:td>Apples</h:td> <h:td>Bananas</h:td> </h:tr> </h:table> <f:tablexmlns:f="http://www.w3schools.com/furniture"> <f:name>African Coffee Table</f:name> <f:width>80</f:width> <f:length>120</f:length> </f:table> </root>

  15. XSL and XSLT • eXtensibleStylesheet Language • eXtensibleStylesheet Language Transformations • Markups for browsers – how to display XML data • most browsers support this • usually irrelevant for non-browser clients • Example

  16. JSON • Same spirit as XML, more concise and much simpler • Textual data (i.e. humans can easily parse it) • Syntactically-valid JavaScript – object literals • User-defined data • Some predefined types • Includes type information with data

  17. JSON simple syntax • object: {} | {members} • members: pair | pair, members • pair: name : value • name: string • array: [] | [elements] • elements: value | value , elements • value: string | number | object | array | true | false | null

  18. JSON example { "Success":true, "Items": [ { "Version":12, "ChildCount":12, "ID":"cbee00bb-1f26-414a-a0aa-9c5a7156fe64", "ParentID":"00000000-0000-0000-0000-000000000000", "OwnerID":"9ffd5a95-b8bd-4d91-bbed-ded4c80ba151", "Name":"Library", "ContentType":"application/vnd.ll.folder”, "CreationDate":1261042614, "Type":"Folder" },{ "Version":0, "ChildCount":0, "ID":"a2bd28c4-9243-418f-887d-4aa219b0046e", "ParentID":"cbee00bb-1f26-414a-a0aa-9c5a7156fe64", "OwnerID":"9ffd5a95-b8bd-4d91-bbed-ded4c80ba151", "Name":"Animations", "ContentType":"application/vnd.ll.animation”, "CreationDate":1261042614, "Type":"Folder" } ] } object object array object

  19. JSON in JavaScript object literal, i.e. textual representation varmyJSONObject = {"bindings": [ {"ircEvent": "PRIVMSG", "method": "newURI", "regex": "^http://.*"}, {"ircEvent": "PRIVMSG", "method": "deleteURI", "regex": "^delete.*"}, {"ircEvent": "PRIVMSG", "method": "randomURI", "regex": "^random.*"} ] }; myJSONObject.bindings[0].method // "newURI” varmyObject = eval('(' + myJSONtext + ')'); varmyJSONText = JSON.stringify(myObject); actual object back to literal

  20. Summary • Understanding of external data representations • why – because heterogeneity happens and we want to interoperate • well-known ones – XDR, XML and JSON • btw, all of this applies to files too! bits  ASCII  syntax  semantics

More Related