Chapter Three Data Compression WinZip Wizard Select Activity what do you want to do? Choose the activity you wish to perform. then click on Neo the Intemet 填少气 OUnzp or natal from an existing Zip He UPdate an exing Zo file Opeate anew Re WANZE Ozo importan ocuments, favorites, emal etc. Unit11 a part 1 Notes to Text L Part4 Extensive Reading Part 2 Word Study Part5 Notes to Passage Part3 Practice on Text Part6 Practice on Passage 2021/2/20 P1
2021/2/20 P.1 Unit 11 Data Compression Chapter Three @ Part 1 Notes to Text & Part4 Extensive Reading & Part 2 Word Study @ Part5 Notes to Passage @ Part3 Practice on Text @ Part6 Practice on Passage
a Part 1 Notes to text Data Compression 1)In com puter science and information theory, data com pression or source coding is the process of encoding information using fewer bits than an unencoded representation would use through use of specific encoding schemes.在计算机科学和信息理论中,数据压缩 或信源编码其实就是指采用比未经编码的信息表现方式更少的字节,通 过专门的编码系统进行编码的过程 注释:此句是主系表句型。 data compression or source coding 是主语, the process of encoding information是表语, using fewer bits和 through use of specific encoding schemes是修饰 encoding information的状语。 than an unencoded representation would use 是比较状语从句。 2)For exam ple, this article could be encoded with fewer bits if one were to accept the convention that the wordcompression"be encoded as"comp".例如,假如我们接受这样一种约定,也即是:将 compression"编译为"comp",那么用较少的位数就可以给这篇文章 完成编码。 注释: if one were to.是条件状语从句,were是虚拟语气,表示假设; that引导的从句是同位语,用以解释 convention的具体内容。 2021/2/20 P2
2021/2/20 P.2 @ Part 1 Notes to Text 1) In computer science and information theory, data compression or source coding is the process of encoding information using fewer bits than an unencoded representation would use through use of specific encoding schemes. 在计算机科学和信息理论中，数据压缩 或信源编码其实就是指采用比未经编码的信息表现方式更少的字节，通 过专门的编码系统进行编码的过程。 注释：此句是主系表句型。data compression or source coding 是主语， the process of encoding information是表语，using fewer bits和 through use of specific encoding schemes是修饰encoding information的状语。than an unencoded representation would use 是比较状语从句。 2)For example, this article could be encoded with fewer bits if one were to accept the convention that the word "compression" be encoded as "comp".例如，假如我们接受这样一种约定，也即是：将 "compression"编译为 "comp"，那么用较少的位数就可以给这篇文章 完成编码。 注释：if one were to…是条件状语从句，were是虚拟语气，表示假设； that引导的从句是同位语，用以解释convention的具体内容。 Data Compression
3)One popular instance of compression with which many computer users are fam iliar is the ZiP file format, which, as well as providing com pression, acts as an archiver, storing many files in a single output file.zP文件格式就是众多计算机使用者都很 熟悉的一种普及型压缩实例,它不但提供压缩,而且充当文件存储器, 在一个ZP输出文件中就可以存放很多文件。 注释:此句是主系表句型。 One popularinstance of com pression 是主语; the zIP file format是表语; with which many computer users are familiar是介词提前的定语从句, which指代前面的 instance of compression; which, as well as providing compression, acts as an archiver, storing many files in a single output file.是非限制性定语从句, which指代前面的 the ziP file format; providing compression/Storing many files in a single output file都是这个定语从句里的状语 2021/2/20 P3
2021/2/20 P.3 3) One popular instance of compression with which many computer users are familiar is the ZIP file format, which, as well as providing compression, acts as an archiver, storing many files in a single output file. ZIP文件格式就是众多计算机使用者都很 熟悉的一种普及型压缩实例，它不但提供压缩，而且充当文件存储器， 在一个ZIP输出文件中就可以存放很多文件。 注释：此句是主系表句型。One popular instance of compression 是主语；the ZIP file format 是表语；with which many computer users are familiar是介词提前的定语从句，which指代前面的 instance of compression；which, as well as providing compression, acts as an archiver, storing many files in a single output file.是非限制性定语从句，which指代前面的the ZIP file format；providing compression和storing many files in a single output file都是这个定语从句里的状语
4)A com pression method called Huffman coding is frequently used in data communications, and particularly in fax transmission有种叫 哈夫曼编码的压缩方法经常被用在数据通信,特别是传真传输上。 注释: Huffmancoding(哈夫曼编码)是一种根据字符出现的概率来构 造平均长度最短的编码。它是一种变长的编码。在编码中,若各码字长 度严格按照码字所对应符号出现概率的大小的逆序排列,则编码的平均 长度是最小的。(注:码字即为符号经哈夫曼编码后得到的编码,其长 度是因符号出现的概率而不同,所以说哈夫曼编码是变长的编码。) 5)Were the letter made up of randomly distributed black ink covering 50 percent of the white paper surface, data compression would hold no advantages.如果构成信件的那些随意分布的黑色墨迹 占据了白纸表面的50%,那么,数据压缩在此时就没什么优势可言了。 注释: Were the letter made up of.= f the letter were made up of…. 在书面语中,条件从句可以不用连词,而将谓语中的过去式were,had 或 should等移至主语前。这属于虚拟语气中的一种特殊结构形式; covering50 percent of the white paper surface是现在分词短语做定语, 修饰前面的 black ink。 2021/2/20 SPaY End
2021/2/20 P.4 4) A compression method called Huffman coding is frequently used in data communications, and particularly in fax transmission.有种叫 哈夫曼编码的压缩方法经常被用在数据通信，特别是传真传输上。 注释：Huffmancoding（哈夫曼编码）是一种根据字符出现的概率来构 造平均长度最短的编码。它是一种变长的编码。在编码中，若各码字长 度严格按照码字所对应符号出现概率的大小的逆序排列，则编码的平均 长度是最小的。（注：码字即为符号经哈夫曼编码后得到的编码，其长 度是因符号出现的概率而不同，所以说哈夫曼编码是变长的编码。） 5) Were the letter made up of randomly distributed black ink covering 50 percent of the white paper surface, data compression would hold no advantages. 如果构成信件的那些随意分布的黑色墨迹 占据了白纸表面的50%，那么，数据压缩在此时就没什么优势可言了。 注释：Were the letter made up of…= If the letter were made up of…。 在书面语中，条件从句可以不用连词if，而将谓语中的过去式were, had 或should等移至主语前。这属于虚拟语气中的一种特殊结构形式； covering 50 percent of the white paper surface是现在分词短语做定语， 修饰前面的black ink。 End
Part 2 Word Study L. representation n.表现法,表现8. alter v.改变 2. convention n.惯例,协定 9 restore v.恢复 3. archiver n.档案存储器 10. procedure n.过程 4. statistically adv.统计上地 1l. decompression n.解压缩 5. character n.字符 12. consecutive string连贯的字符串 6. binary ad.二进位的,二元的13. randomly distributed随意分布的 7. assign -V.赋值,指定 2021/2/20 P.5 End
2021/2/20 P.5 End 1. representation n. 表现法，表现 8. alter v. 改变 2. convention n. 惯例，协定 9. restore v. 恢复 3. archiver n. 档案存储器 10. procedure n. 过程 4. statistically adv. 统计上地 11. decompression n. 解压缩 5. character n. 字符 12. consecutive string 连贯的字符串 6. binary adj. 二进位的，二元的 13. randomly distributed 随意分布的 7. assign v. 赋值，指定 & Part 2 Word Study
Part3 Practice on Text Task 1: Listening training Dictation of some key words Directions: You will hear some key words twice, most of which are taken from the Word Study. Then finish the Crossword Puzzle. ( See you book p. 2. Dictation of some key expressions Directions: You will hear some key expressions twice, most of which are taken from this text. Then you are asked to complete the missing words 1)data compression_4)anuncompressedmessage 2)encoding information 5)in faxtransmission 3)asingle output file) randomly distributed-blackink 2021/2/20 P.6
2021/2/20 P.6 Task 1: Listening training Dictation of some key words Directions: You will hear some key words twice, most of which are taken from the Word Study. Then finish the Crossword Puzzle. (See you book p. ) 2. Dictation of some key expressions Directions: You will hear some key expressions twice, most of which are taken from this text. Then you are asked to complete the missing words. @ Part3 Practice on Text 1) data________________ 2) ___________information 3) a single_______________ 4) an ___________________message 5) in fax___________________ 6) ______________________black ink compression encoding output file uncompressed transmission randomly distributed
Task 2. Read. Write and Translate Read and Reply Directions: Students are required to read aloud the whole text after the teacher. Then give short answers to the following questions a) What is data compression? Data compression is the process of encoding information using fewer bits than an unencoded representation would use through use of specific encoding schemes b) What would be discovered if a ty pical message were statistically analyzed? If a typical message were statistically analyzed, it would be found that certain characters are used much more frequently than others c)Can all kinds of data be compressed to the same degree? No 2021/2/20 P7
2021/2/20 P.7 Read and Reply Directions:Students are required to read aloud the whole text after the teacher. Then give short answers to the following questions: a) What is data compression? b) What would be discovered if a typical message were statistically analyzed? Task 2: Read, Write and Translate Data compression is the process of encoding information using fewer bits than an unencoded representation would use through use of specific encoding schemes. If a typical message were statistically analyzed, it would be found that certain characters are used much more frequently than others. No. c) Can all kinds of data be compressed to the same degree?
Read and Judge (F1) Data compression or source coding is the process of encoding information using more bits than an unencoded representation would use through use of specific encoding schemes (F)2) The zIP file format only provides compression (F)3) By analyzing a message before it is transmitted, longer binary codes may be assigned to frequently used characters and shorter codes to rarely used characters. (T)4) Data representing a com puter program may not be reduced significantly. (F )5) Huffman coding can help reduce the total message length for any faxed business letter. G20212120P8G End 1
2021/2/20 P.8 ( )1) Data compression or source coding is the process of encoding information using more bits than an unencoded representation would use through use of specific encoding schemes. ( )2) The ZIP file format only provides compression. ( )3) By analyzing a message before it is transmitted, longer binary codes may be assigned to frequently used characters and shorter codes to rarely used characters. ( )4) Data representing a computer program may not be reduced significantly. ( )5) Huffman coding can help reduce the total message length for any faxed business letter. Read and Judge End F F F T F
Read and Complete Directions: Read the following short passage. Complete it by filling in the missing words A require B enough C useful D detrimental E involve F compress G such H including decompressed J instance Compression is 1.C because it helps reduce the consumption of expensive resources, 2)G as hard disk space or transmission bandwidth On the downside, compressed data must be 3)I to be viewed, and this extra processing may be 4)D to some applications For 5) a compression scheme for video may 6) Expensive hardware for the video to be decompressed. fast 7) Bto be viewed as it's being decompressed. The design of data thdidegree of com pression, the amountor. srious com pression schemes therefore 8) t Ade-offs among va factors, 9) distortion introduced, and the com putational resources required to 10)F and uncompress the data 2021/2/20 .9y End
2021/2/20 P.9 Directions:Read the following short passage. Complete it by filling in the missing words. A. require B. enough C. useful D. detrimental E. involve F. compress G. such H. including I. decompressed J. instance Compression is 1_____because it helps reduce the consumption of expensive resources, 2）_____as hard disk space or transmission bandwidth. On the downside, compressed data must be 3）___ to be viewed, and this extra processing may be 4）___ to some applications. For 5）______，a compression scheme for video may 6） _____expensive hardware for the video to be decompressed fast 7） _____to be viewed as it's being decompressed. The design of data compression schemes therefore 8）_____trade-offs among various factors, 9）______the degree of compression, the amount of distortion introduced, and the computational resources required to 10）_____and uncompress the data. Read and Complete End C G I D J A B E H F
Read and Translate Directions: Put the following sentences into English, using the words or phrases given 1)他们抛弃了过去的习惯。( convention) They abandoned the conventions of the past. 2)我们使他恢复原职。( restore) We restored him to his old post 3)魔术师叫我随便挑一张牌。( at random) The magician asked me to pick a card at random 4因为下大雨,我们不得不改变计划。(ater) We had to alter the plan because of the heavy rain 5)那件工作分配给我了。( assign) The task was assigned to me 202120P10 End
2021/2/20 P.10 1)他们抛弃了过去的习惯。（convention） 2)我们使他恢复原职。（restore） 3)魔术师叫我随便挑一张牌。(at random) 4)因为下大雨，我们不得不改变计划。(alter) 5)那件工作分配给我了。(assign) Read and Translate Directions:Put the following sentences into English, using the words or phrases given. End They abandoned the conventions of the past. We restored him to his old post. The magician asked me to pick a card at random. We had to alter the plan because of the heavy rain. The task was assigned to me