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E-Genting Programming Competition 2005. Public Lecture by Jonathan Searcy 21 January 2006. Competition Questions. Failsafe Storage. An application programmer required a small amount of failsafe storage; The storage had to be completely updated or completely unchanged;
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E-Genting Programming Competition 2005 Public Lecture by Jonathan Searcy 21 January 2006
Failsafe Storage • An application programmer required a small amount of failsafe storage; • The storage had to be completely updated or completely unchanged; • If the power failed during a write, the update had to be rolled back.
Where did the Contestants have Difficulty? • getting the data into and out of the disk files; • calculating and validating the CRC; • evaluating the modulo 232 comparison.
The Nature of Magnetic Storage FM Encoding Scheme for Magnetic Media
Initialisation Write-function pseudo-code: 1. If the class is not initialised: a. Execute a read cycle to discover the latest serial number and which of the two files was last updated. 2. Increment the serial number. 3. Create a byte array of the data to be written. 4. Write the byte array to the file that was least recently updated.
Summary • The nature of computer storage and thesystem calls for transferring binary data. • The distinction between formatting and input/output. • The nature of a CRC and some of its properties. • The effects of storing data in different sequences. • The nature and consequences of the two’s complement integer format. • Various characteristics of modular arithmetic. • The need to consider initialisation.
Mytel Mobile • Mytel Mobile operates a mobile telephone service. • Subscribers can earn points by making calls on their mobile phones. • Mytel wants to set up a point redemption arrangement with an airline so that its subscribers can exchange points for flights. • To convince the airline to enter into the arrangement, Mytel needs a report that displays the destination and frequency of its subscribers’ flights. • Mytel has a database that contains information about each call, including the identity of the subscriber, the time of the call and the city from which the call was made.
Data Dictionary • date and time the report was generated; • reporting period (from-date and to-date); • for each point balance range: • the point balance range; • number of subscribers; • for each base city: • for each other city: • number of trips; • total number of trips; • totals for all point balance ranges.
Errors that an embedded SQL pre-processor can detect at compile time that raw JDBC calls cannot detect until run time: incorrectly spelled reserved words such as ‘select’ and ‘where’; syntax errors in SQL statements; misspelled column names; ambiguous column names (i.e. a reference to an unqualified column name that is a valid column name in two tables in the query); incompatible database column and host variable data types.
Client and Server-Mode Processes • Client-mode processes execute top-to-bottom. When they need to communicate with another process they call a function to transfer the data. • Server-mode processes wait in an idle state to be called by a client-mode process. When called, they perform whatever function is needed and then return control to the client-mode process.
Summary • Data dictionary interpretation; • Report layout interpretation; • Database accessing using SQL; • Dataflow analysis; • Using parallel processing to overcome serial throughput constraints; • Converting top-to-bottom pseudo-code into an event-driven finite state machine.
Project Scheduling Program • accept an input file name as an argument; • read and analyse the input file; • generate a project schedule listing.
Token Types • words (keywords, task names, person identifiers, numbers and dates); • strings (task descriptions); • semicolon; • comma; • open brace; • close brace; • end-of-file.
