Transcript Database
Mgt 20600: IT Management & Applications Networks (cont.) Databases Thursday October 13, 2005 Reminders Reading – For today Fundamentals text, Chapter Three, Organizing Data and Information chapter – For the Thursday after break Fundamentals text, Chapter 6, Information and Decision Support Systems Homework – Database/DSS homework will be posted tomorrow – Due October 28th: Friday after fall break Exams – Medians of 58.6 (Section 3) and 59.5 (Section 4) Nice work for many of you! If you didn’t do as well as you like, still many hundreds of points to go in the course Suggestions – Always do reading ahead of time, not just before exam – Always come to class – Take the homeworks seriously and review them before the exams – Come and see me and Christine for help with exam review Next week: Fall break! Telecommunications and Networks Elements of a Telecommunications System Transmission Media Wired Transmission Media Types Wired Media Types Wireless Transmission Media Types Radio Waves – Bluetooth Short distances only Relatively slow transmission speed Developed for inter-device communications – Wi-Fi Standard supports up to 54Mbps Supports longer distances than bluetooth Infrared – Signals sent as light waves – Short distance – Unobstructed line of sight Microwave – – – – High frequency radio signal Capable of high-speed transmission Unobstructed line of sight Susceptible to interference Cellular Networks Computer network: the communications media, devices, and software needed to connect two or more computer systems or devices Network nodes: the computers and devices on the networks Network Types Personal area network (PAN) Local area network (LAN) Metropolitan area network (MAN) Wide area network (WAN) International network Network Types A Typical LAN Network Types Is the internet a wide area network? A Wide Area Network Communications Software and Protocols Communications software: software that provides a number of important functions in a network, such as error checking and data security – Network operating system (NOS) – Network management software – Communications protocol: a standard set of rules that controls a telecommunications connection Example, TCP/IP protocol that underlies the Internet The Internet Internet: a collection of interconnected networks, all freely exchanging information ARPANET – The ancestor of the Internet – A project started by the U.S. Department of Defense (DoD) in 1969 How the Internet Works Data is passed in chunks called packets – Internet Protocol (IP) Communications standard that enables traffic to be routed from one network to another as needed Every computer attached to internet has an IP address – Transmission Control Protocol (TCP) Widely used transport-layer protocol that is used in combination with IP by most Internet applications In charge of communication session between two computers – Uniform Resource Locator (URL) Assigned addresses for web servers and the web pages they provide How the Internet Works Routing Messages over the Internet Accessing the Internet Several Ways to Access the Internet Internet Service Providers Internet service provider (ISP): any company that provides individuals or organizations with access to the Internet – Most charge a monthly fee – Many ISPs and online services offer broadband Internet access through digital subscriber lines (DSLs), cable, or satellite transmission Applications that run over the Internet World Wide Web Instant Messaging Email File Transfer Protocol Telnet All of these are – Software applications – Designed for the internet – All assume your computer understands TCP/IP The World Wide Web Hypertext Transfer Protocol (HTTP): Protocol that web servers and browsers use to send requests and information Hypertext Markup Language (HTML): the standard page description language for Web pages Intranets and Extranets Intranet – Internal corporate network built using Internet and World Wide Web standards and products – Used by employees to gain access to corporate information – Slashes the need for paper Intranets and Extranets Extranet – A network based on Web technologies that links selected resources of a company’s intranet with its customers, suppliers, or other business partners Virtual private network (VPN) – Secure connection between two points across the Internet – Intranets and extranets often run over VPN’s Internet Issues Privacy – Spyware: hidden files and information trackers that install themselves secretly when you visit some Internet sites – Cookie: a text file that an Internet company can place on the hard disk of a computer system Net Issues Security – Cryptography: converting a message into a secret code and changing the encoded message back to regular text – Digital signature: encryption technique used to verify the identity of a message sender for processing online financial transactions – Firewall: a device that sits between an internal network and the Internet, limiting access into and out of a network based on access policies Net Issues Databases A well-designed and well-managed database is an extremely valuable tool in supporting decision making Databases are key corporate assets Databases are the foundation for sophisticated analyses that provide business intelligence – What new products to design – How to market to particular customer groups – Which customer groups are the most profitable Traditional Approach to Data Management Traditional approach: separate data files are created for each application Results in data redundancy (duplication) Data redundancy conflicts with data integrity Database Approach to Data Management Database approach: pool of related data is shared by multiple applications Significant advantages over traditional approach Advantages of Database Approach Improved strategic use of data Reduced data redundancy Improved data integrity Easier modification and updating Data and program independence Better access to data and information Standardization of data access A framework for program development Better overall protection of the data Shared data and information resources Disadvantages of the Database Approach More complexity More difficult to recover from a failure More expensive Databases Databases must contain – Accurate information – Right kinds of information – Current information – Information from all organizational functions Database Data Data regarding – Important entities Customers Suppliers Transactions – Each entity will have a number of attributes about which you want to collect and store information Customer address Customer phone number Customer account number Entities, Attributes, Keys Entity: a generalized class of people, places, or things (objects) for which data is collected, stored, and maintained (Table and records) Attribute: a characteristic of an entity (fields) Data item: a value of an attribute (fields) Key: field(s) that identify a record Primary key: field(s) that uniquely identify a record Hierarchy of Data Field: name, number, or characters that describe an aspect of a business object or activity Record: a collection of related data fields File: a collection of related records Database: a collection of integrated and related files Data Modeling and the Relational Database Model When building a database, consider: – Content: What data should be collected, at what cost? – Access: What data should be provided to which users, and when? – Logical structure: How should data be arranged to make sense to a given user? – Physical organization: Where should data be physically located? Data Modeling Building a database requires two types of design – Logical design Shows an abstract model of how data should be structured and arranged to meet an organization’s information needs – Physical design Fine-tunes the logical database design for performance and cost considerations Data Modeling Data model: a diagram of data entities and their relationships Entity-relationship (ER) diagrams: data models that use basic graphical symbols to show the organization of and relationships between data Data Modeling An Entity-Relationship (ER) Diagram for a Customer Order Database The Relational Database Model Relational model: all data elements are placed in two-dimensional tables (relations), which are the logical equivalent of files In the relational model: – Each table represents a data entity – Each row of a table represents a specific instance of a data entity – Columns of the table represent attributes The Relational Database Model A Relational Database Model