Notes, summaries, assignments, exams, and problems for Computers

Object Identity Types

There are three main types of object identity:

• Asset (Data Value as Identity): This form of identity, commonly used in relational systems, utilizes a data value as the identifier. For instance, the primary key value in a tuple uniquely identifies that tuple.
• Name (User-Defined Identity): This type of identity relies on a name assigned by the user. File systems often employ this approach, where each file has a unique name regardless of its content.
• Incorporated (System-Generated Identity): This concept integrates identity directly into the data model or programming language, eliminating the need for user-provided identifiers. Object-oriented systems commonly use this method, automatically assigning a unique identifier to each

Operating System (OS)

Software that manages hardware resources and provides a high-level abstraction for the user.

Process

A program currently executing.

Multitasking System

An OS allowing multiple programs to run concurrently.

Multiuser System

An OS allowing simultaneous access for multiple users.

Command Interpreter (Shell)

A user interface program that executes commands.

System Calls

Interfaces (APIs) used by programs to request services from the OS.

Single-Tasking System

Allows only one job in memory at a time. The CPU is idle during I/O operations, as it cannot be used by another process when the current one accesses system resources.

Time-Sharing System

Allows multiple terminals connected to a central computer. Enables multiple processes to use the... Continue reading "Operating System Core Concepts" »

Gantt Chart: A Project Planning and Control Method

A Gantt chart is a graphical method of planning and control in which a project is divided into different activities, and estimates are made about how long each activity takes. This chart shows the timing relationships between events of a program and was developed by Henry L. Gantt. Gantt charts are useful for monitoring relatively small projects.

Understanding Key Concepts

• Task: Project activities are carried out in a particular sequence.
  • Predecessor Task: A task that must start or finish before another can begin.
  • Successor Task: A task that depends on the start or finish of a preceding task.
  • Summary Tasks: These are made up of subtasks and summarize those subtasks.
• Milestones: A task without duration

Virtual machines are software that emulates a computer and can run programs like a real computer. This software was initially defined as "an efficient, isolated duplicate of a physical machine." The meaning of the term now includes virtual machines that have no direct equivalence with any actual hardware.

Understanding Shells

A shell is a piece of software that provides an interface for users. Usually, the term refers to the operating system shell that provides access to kernel services. The operating system shells generally fall into two categories according to their interface:

• Command Line Interface (CLI)
• Graphical User Interface (GUI)

Multiprogramming vs. Monoprogramming

Multiprogramming allows two or more processes to run in the same unit of

Software Validation and Verification Fundamentals

Objectives of Validation and Verification

• Detect and correct defects as soon as possible.
• Reduce risks of budget and timetable deviations.
• Improve software quality and reliability.
• Improve development process management visibility.
• Quickly assess proposed changes.

Philosophy of Software Testing

Recommendations by G.J. Myers:

• Each test case should define the expected output.
• Programmers must avoid testing their own programs.
• Thoroughly inspect test results to identify possible symptoms of defects.
• Test case generation should include valid, invalid, and unexpected inputs.
• Prove that the software performs as intended and avoids unintended actions.
• Test plans should always assume the presence of defects to avoid

Creating Engaging Multimedia Presentations

A presentation is a multimedia file that can contain text, graphics, photos, music, and video. Its organization is done by slides, which succeed one another under your control. Templates are presentations that have predefined design objects in the slides, such as the background, fonts, placement of text, and other objects that give the presentation a common appearance across all slides.

Interactivity: Establishing Hyperlinks

Interactivity is established by creating hyperlinks. Clicking on a button or text performs an action, such as opening a file or linking to a website. You can insert a hyperlink from the Insert menu, then selecting Hyperlink.

Interactivity in objects allows navigation to different slides... Continue reading "Creating Engaging Multimedia Presentations" »

Computer Science Fundamentals

Informatics is the science or technical study of technology that enables the automatic processing of information using electronic devices and computer systems.

Hardware and Software

• Hardware: All the physical parts that compose a computer.
• Software: A set of programs that execute tasks using the electrical circuits of the computer.

Software Types:

• System Software
• Software Development
• Application Software

Numbering Systems

• Decimal System: Each figure has a weight where its value depends on its location.
• Binary System: The most elementary coding system, using only "0" and "1". This coding avoids confusion in electronic systems because they identify only two possible states.

Bits and Bytes

A bit is an electronic signal that can... Continue reading "Computer Science Fundamentals and Programming Basics" »

Parbegin / Person Learns

Parbegin is a structure to indicate parallel execution, marking the beginning and end. Selection: A statement dividing sequential execution into parallel streams.

Its general form (Dijkstra):

parbegin Proposition1; Proposition2; Proposition n; person learns

Mutex

Mutex occurs when processes share data, preventing simultaneous access. It applies when a process accesses shared data, allowing concurrent execution of non-conflicting transactions.

Critical Sections

A process accessing shared data is in a critical section. When a process is in a critical section:

• All other processes are excluded from their critical sections.
• Other processes can execute outside their critical sections.
• When a process exits, the next waiting process