Andy presented another high paced lecture this week, the theme was Deadlock and Inter-Process Communication. This is a continuation of the Process Management topic from last week.
As a recap:
Deadlocks: Can occur on any multitasking O/S where a single process is given exclusive access to a file, device or resource. Detailed conditions:
Mutual Exclusion – One process can hold a resource exclusively
Hold and Wait – A process can request a new resource over time whilst still holding other resources.
No pre-emption – resources can only be released by the program that is holding them
Circular Wait – 2 or more processes waiting for resources held the other processes.
Manoj presented lecute number 7 this week, titled “SQL III”. True to the title, we churned through 2 hours of SQL definitions and examples. Interestingly there are a number of differences between Oracle and MySQL. To really get the hang of SQL I have just set up a MySQL server on my home PC and running over the commands show in the lectures/tutorials and in the Text book.
This makes me wonder why Oracle is a such a superior option over other (is the actual product better?). On some further investigation (of Oracle’s wikipedia page: http://en.wikipedia.org/wiki/Oracle_Database)there may be a couple of major reasons:
Oracle Corporation claims to have provided:
the first commercially-available SQL-based database (1979)[38]
After finishing our lecture on Use Case Diagrams and Class Models, David completed a lecture titled “Finishing Analysis”.
This stage can be broken down into:
Prioritizing System Requirements -> Describe relevant strategic decisions required for implementation -> Determine alternative approaches for development -> Evaluate and Select an approach -> Write up request for proposal and evaluate vendor proposals (should be prior to selecting approach?) ->Present findings to management.
Put simply the final stage of analysis is to (along with management) decide on what Design, Implementation and Support path will best suit the needs of the organization.
* Gather information (review documents, current practices, conduct interviews, prototyping, questionnaires, JAD sessions, Vendor Solutions)
* Define System Requirements
-> * Prioritize Requirements
-> * Prototype (feasibility and discovery)
-> * Generate and evaluate alternatives
-> * Review with management
These 4 final steps really are just drawing a conclusion from the information gathered in the Planning phase and earlier Analysis phase steps.
Pearl of the week: In the final stages of Analysis with presentations to management it is very easy to respond ‘Yes’ to management requests which would result in serious ‘scope creep’. Ensure the solution will solve the key issues with the resources allocated (this is superior to attempting to solve everything with more than the allocated resources).
When determining alternatives, particularly for businesses, a tiered approach is best; Low Automation and cost, Mid Automation and Cost, High automation and cost. In presenting/selecting alternatives the POSTEL analysis method is relevant as a ‘big picture’ view is necessary.
Build or Buy? Buy will become increasingly prevailent
A bit of a late entry for last weeks classes. The lecture was once again presented by Michael Smith and this week we ran through a number of Java (and programming) basics.
Library Classes – Java API, API documentation is generally the first google results when you search a method/data type + ‘JAVA’
Collections – Arrays and ArrayLists is a types of collection
Dynamic Arrays – called ‘ArrayList ‘ in Java (there may be other collections in Java? but ArrayList the only one I know of). Much better than arrays in that the size is dynamic and objects can be stored and all iteration and sorting is pretty much already optimized. Java’s for-each loop – for(Elementtype element : collection) – for (String note : noteBook)
Process Management was the theme of Andy’s lecture this week. Specifically, a definition of processes and how they intersect with the CPU, Process Control and Process Scheduling Algorithms.
Processes – Simply a program execution.
Process Control – an import part of a multi-tasking O/S (modern O/S’s and CPUs enable multithreading)
Information about processes is store in the Process Table by the O/S
The lecture glazed over the process management system stopping at:
Manoj presented a lecture focused on the Structured Query Language [SQL] upon our return from the easter break. The tutorial was closely tied to the lecture enabling us to work through the code examples shown. With that in mind, shown below are the types of queries covered in the lecture and tutorial with an example and description:
CREATE – create tables (or Databases), specifying the table name and column values. Constraints can be applied to the attributes such as Primary Key, Foreign Key, Default value and Not Null however it is probably easier to add constraints using the ‘ALTER TABLE’ query. CREATE is part of DDL.
CREATE TABLE DEPARTMENT
(DEPT_NUM INTEGER, DEPT_NAME varchar(20), CREATION_DATE DATE);
After a weeks break David presented an introductory lecture on the Object Oriented Analysis Phase [PADIS]. As we had already covered Class Diagrams in the previous lecture we moved straight into Use Case Modeling. All of the diagrams used in the Object Oriented Analysis phase (and discussed in this week) are members of the Unified Modeling Language:
Source: Paulo Merson
The Diagrams/Models covered in the Object Oriented Analysis phase are:
This weeks lecture was presented by Michael Smith and targeted an introduction to testing and debugging. Initially was discussed when testing should begin in the Software Development process, the Design phase. As soon as the solution has been designed then tests for that solution can and should also be designed. During the implementation phase testing should be conducted as soon as compilation is complete. Documentation was also recognized early in the lecture as a key aspect of testing and debugging.
Pearl Of The Week: Types of errors in Programs:
Syntax Errors -> Mistakes in spelling or unclosed parenthesis etc. Compiler will find these errors, preventing completion of compilation until they are amended.
Execution/Run Time Errors -> Null Pointer Exceptions, Attempting to access arrays outside of bounds. Occurrence of these errors in Java will result in relevant exceptions thrown.
Logic Errors -> Project has been compiled and runs without error but behavior is not as expected.
We then explored some examples of how important testing and debugging is by reviewing some examples where the process was not done correctly.
Virtual Memory enables programs running on an O/S to interact with what to them is a contiguous memory source. That is, program instructions and resources can be loaded to Virtual Memory addresses and a program can easily access them with logical addresses. The illustration above shows a simplified concept of Virtual Memory.
There are two major implementations for Virtual Memory:
Database Design III – Boyce Codd Normal Form, presented by Manoj Kathpalia, alerted me to the value of revising the text book. It seems I do not have a clear grasp of some of the characteristics of each Normal form. Must ensure to remember that for a relation to be in BCNF every functional dependency must be a candidate key, this is best illustrated graphically:
source: Database Systems, Cornell and Rob, 2009
So, although the iPhone pic of the text book is a bit blurry, it can be seen that a sneaky dependency from a non-candidate key attribute to another attribute will cause update anomalies and refrain the table from achieving BCNF.
Most of the lecture was focused on ensuring that everyone understood the process of 1NF -> 2NF -> 3NF -> BCNF. I have already made a detailed post on this process which can be viewed here.
Our tutorial was 2 hours of toying with MicroSoft Access. I came into it with an open attitude, but after about 90 minutes I was lost in the world of GUI fluff that is Access. I am sure that with time it is something that one could learn to use with more efficiency, but with superior performing Open Source alternatives (ie: LAMP bundle) I cannot ever see myself working on an Access database by choice.
Pearl of the Week: Avoid Microsoft Access.
I plan to review the text book over the next week to ensure that my current perception of each aspect of the subject is in fact valid. Particularly important is to rote learn definitions for 1NF, 2NF, 3NF, BCNF, Functional Dependency, Transitive Key Dependency(3NF), Partial Dependency (2NF) and Non-Key Partial Dependencies (BCNF).
