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

1. Data Models and Conceptual Schemes

The conceptual scheme within the ANSI/X3/SPARC framework aims to define the data and the relationships between them that will be computerized in a particular organization, subsequently translating this into a canonical schema. The primary challenge is defining the set of entities to be stored in the database (DB), a task dependent solely on the Database Administrator (DBA).

Recall the three conceptual models, often called semantic models:

• MER (Entity-Relationship Model)
• Binary Model
• RMT (Semantic Model)

Once the conceptual design is complete, the process moves to the logical design or definition of the canonical schema. This translation process is performed using logic models, also known as data models. The most... Continue reading "Database Fundamentals: Comparing Relational, Hierarchical, and Network Models" »

Core Concepts: Domain, Attribute, and Entity

Domain: A set of values of any simple or elemental type which can represent the possible values a variable takes for a characteristic or property (attribute) of a representable object (entity).

Attribute: Anything capable of taking a value (data) within a domain (range of possible values). Attributes sharing the same domain are typically given the same or similar names to avoid confusion.

Entity: Anything that can hold a set of attributes with occurrences in the universe. Each occurrence is assigned values for each attribute. More formally, an entity is a set of attributes A₁, A₂, ..., A_n, taking values in their respective domains D₁, D₂, ..., D_n.

Understanding Relationships and Relations

A relationship... Continue reading "Relational Database Fundamentals: Entities and Attributes" »

Web Engineering Models

Data Model

Compatible with the entity-relationship model and UML class diagrams.

Hypertext Model

• Composition: Site pages, content units of pages.
• Unit: Atomic content element, used to publish the information specified in data models.
• Navigation: Specified by links.
• Links: Between units of a page, between units of different pages, or between pages.
• Defines both the content and navigation.

Presentation Model

• The appearance of web pages.
• Does not include specific elements for conceptual modeling; notations are used.
• XML.
• The presentation is specified using XSL stylesheets.

Web Engineering UML-Based Methodology (UWE)

• Proposal based on UML and the Unified Process, adapted to the web.
• Specific object-oriented techniques are used.
• Proposes an

History of Windows NT

Windows NT was originally developed to be OS/2 3.0 before Microsoft and IBM discontinued their work on OS/2.

• Unlike Windows 3.1, which was a GUI running on MS-DOS, Windows NT is a standalone operating system.

It is based on a microkernel, supporting up to 4GB of RAM, FAT file systems, NTFS, HPFS, built-in network support, multiprocessor support, and C2 security.

Windows NT Features

• It is based on variations of the kernel of Mac UNIX. The microkernel architecture supports applications not originally designed for Windows NT.
• It manages basic operations systems and other layers above them.
• Supports five subsystems: Windows 32-bit, 16-bit Windows, DOS, POSIX, and OS/2.
• Functions as a Client-Server in a network environment.
• Allows development

Storage Devices

Storage Devices: devices that store information. They comprise:

Magnetic Disks

Magnetic disks: Hard drives, floppy disks have large capacity, non-volatile random access, but live slower. It is a closed box, partly comprising:

• Platters: Stored information resides here.
• Head: Reads and writes on the platters.
• Motors: Spin the platters and move the heads.

Components of Magnetic Disks

Platters: Glass, ceramic, or aluminum; joined by a shaft and a motor to rotate at 3600 and 7200 rpm, with a diameter of 5.5 inches.

Heads: Magnetic sensor that reads the charge and a magnet to change the charges for writing.

Spindle (Topic): Support for the disks.

Actuator: The motor that moves the heads.

Structure and Organization

Tracks (Structure-Runs): Concentric... Continue reading "Understanding Computer Storage Devices and Media" »

Fundamentals of Information Security

Core Security Principles

• Confidentiality (Privacy): Ensures information is not accessible to unauthorized individuals.
• Integrity: Guarantees information can only be modified by authorized personnel.
• Availability (Operability): Ensures information is accessible and usable when needed.

Common Information Security Threats

Software and System Vulnerabilities

• Bug: An error or flaw in a computer program or system that causes it to produce an incorrect or unexpected result, or to behave in unintended ways.
• Trojan: A type of malware that disguises itself as legitimate software, allowing external users unauthorized access to a computer system.

Network and Data Attacks

• IP Spoofing: The act of creating Internet Protocol (IP)

Criteria to organize files · quick-access necessary when a single record is accessed. -not needed if a file will be processed in batches. Easy to update-a file on CD-ROM updates and never ease storage is not considered economic. -minimum data redundancy. -redundancy can be used to speed up access. · a single-index · Maintenance cheaper. -fewer errors.· Reliability A directory can have subdirectories, thus forming a hierarchical structure in the shape of an inverted tree, is symbolized by a bar of division (/) Some directories on Linux: • / bin Contains executable programs that are part of the Linux operating system . Many Linux commands like cat, cp, ls, more and tar are located in this directory. • / bootIt contains the kernel (or... Continue reading "Parcial_2_antonio_B" »

Network Topologies

Ring Topology

Connects hosts in a physical ring. The last host connects to the first.

Star Topology

Connects all cables to a central point.

Extended Star Topology

Connects individual stars using hubs or switches, extending network coverage.

Hierarchical Topology

Similar to extended star, but uses a computer to control traffic instead of hubs/switches.

Mesh Topology

Provides maximum protection by connecting each host to others, ensuring service continuity.

Network Communication Methods

Broadcast

Each host sends data to all others on the network. Access is first-come, first-served (e.g., Ethernet).

Transmission Tokens

Controls access via sequential token transmission. Hosts send data when they have the token (e.g., Token Ring, FDDI).

Network

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ArcView Project Manager Components

The ArcView Project Manager organizes geographic data through several core components:

• Views: Geographic data organized into interactive maps, each featuring an exclusive table of contents.
• Tables: Tools to manage and manipulate attribute databases.
• Statistical Graphs: Features to develop and display data visualizations.
• Layouts: Flat compositions for printing, incorporating various graphical elements. These "intelligent" map compositions maintain a live link to the underlying data.
• Scripts: Programmed frames written in Avenue, the native programming language and development environment for ArcView.

Accessing the Legend Editor

You can access the legend editor for a theme using these three methods:

1. Double-click the