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File transfer protocols

Extracts from this document...

Introduction

File transfer protocols File transfer is the process of transmitting complete files from one computer to another. To achieve a successful transfer, both sending and receiving devices must establish the protocol (set of rules) by which they will communicate. Various protocols are commonly recognised but they vary in their performance and suitability for particular tasks. Some examples are described below. FTP File Transfer Protocol (FTP) allows large amounts of information to be transferred between computers very conveniently. FTP originated with the UNIX operating system and was to transfer files of all types between remote computer systems. A popular application of is for the uploading and downloading of Web site pages. ASCII This is only appropriate for text files, which contain no control characters. Thus it cannot be used to transfer files produced with a word processor, spreadsheet or graphics package. Neither can it transfer command (COM) or executable (EXE) files, or files in compressed (ZIP, for ex) form. Apart from this, the protocol is not good at controlling errors. Xmodem A file-transfer protocol used for asynchronous communications. It is commonly used in communications packages. The Xmodem protocol transfers data in blocks of 128 bytes, giving each transmitted frame a sequential block number; this number is used to identify the location of errors. A checksum (see Block Check Characters) is attached to each block to check transmission errors. Its ability to find and correct errors makes it suitable for the transfer of files, which must retain their integrity, such as program files. Zmodem Is one of the most advanced protocols, being much faster than Xmodem. Its error correction controls are absolutely reliable. CCITT V42bis This protocol includes a data compression (through encoding, data is reduced in volume) technique and error detection and correction. Both the sending and receiving modem must possess the error correction facility. Implementation Top Down implementation is one way to achieve implementation of software. ...read more.

Middle

The types of tests which should be considered for a system are as follows Inputs- form design (ease of use) - data transmission - input validation and correction Files- empty files - addition/deletion/update - access - controls/security Outputs- output documents/screens - recipient understanding ComputerProcedures- program linkages - operating procedures - recovery and security - timings Clerical Procedures- effects on other systems - user understanding - error correction - timings User Education and Training The success of a new system is very much dependent on the attitudes of the people who use it. Education aims to convince users of the benefits of the system to themselves, their department and the company. Management policy regarding re-deployment ,redundancy etc should be clearly stated. while casualties may result from the introduction of new systems, there are also many positive aspects such as ? reducing very boring clerical activities ? upgrading of skills ? ? improving job satisfaction ? d? Education, therefore, complements and is a pre-requisite to training. e? Training enables users to understand their role in the new system, and prepares them for their own specific tasks. The users and people affected by the new system must be trained, and arrangements for release from normal duties must be made. Many different methods of training are available including f? formal lectures a? ? discussions/seminars ? computer-assisted training (tutorial packages,help facilities etc) ? user manuals/quick reference guides ? Usually a combination of methods will be chosen with an emphasis on 'hands on' experience. Timing and pacing of training is also important, too early and users may forget aspects or become disinterested, too late and users will become flustered. Training does not cease with implementation, but must meet needs of new staff and system changes. changeover Implementation may involve change from a manual system to a computer system or from one computer system to an other. In both cases the system data and procedures require to be changed. ...read more.

Conclusion

If you create a validation rule for a field Microsoft Access doesn't normally allow a Null value to be stored in the field. If you want to allow a Null value add Is Null to the validation rule as in "<>8 Or Is Null". Query criteria in MS Access Field Data Field data finds an exact match for a field Smith will find smith - Access is not case sensitive wildcards Two wildcards can be used to replace field characters. any single character 0 any character B* will find values beginning with B */*/91 will find all dates in 1991 Range Operations ? Sm?th will find Smith and Smyth > greater than < less than >= greater than or equal to >=l0000 finds values greater than or equal to �10000 <= less than or equal to <=#01/12/92# finds values greater than or equal to 01/12/92 Compound Criteria The user can specify more than one example and criteria at any one time, Multiple examples fall into two categories; AND - OR situations AND All conditions specified must be satisfied before access displays data OR At least one of the conditions specified before data is shown Special Operators Date () will extract records with today's date Like Will extract records similar to eg, 'Like Peters*' will extract surnames similar to Peters NOT finds records not matching the condition, eg Not Smith will exclude records NULL extracts records with a blank field Summary Fields in MS Access Operator Function SUM calculates total value in field AVG calculates the' average value COUNT counts the number of records MIN finds the lowest value MAX finds the highest value H. T. Harvey 24 Dec 2000 H. T. Harvey 24 Dec 2000 H. T. Harvey 24 Dec 2000 H. T. Harvey 24 Dec 2000 H. T. Harvey 24 Dec 2000 H. T. Harvey 24 Dec 2000 H. T. Harvey 24 Dec 2000 H. T. Harvey 24 Dec 2000 H. T. Harvey 24 Dec 2000 H. T. Harvey 24 Dec 2000 ...read more.

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