1 database concepts

Integrity controls protect the database from authorized but invalid operations. Now, when I say a figure like Figure 1-1 “shows ... a typical database,” what I mean is it shows that database as perceived by the user (what’s sometimes called a logical database). About Relational Databases. Changes in This Release for Oracle Database Concepts. What columns do they involve? b. Assignment 2: Database Concepts Part 1: MS Access The following ERD shows the entities included in a database system along with their relationships. For example, see the variable definitions—i.e., the VAR statements—in Figure 1-3. Concurrency controls are intended to take care of such issues, and I’ll have more to say about them in Part II of this book. For a row, each column must have an atomic value, and also for a row, a column cannot have more than one value. A relation having three attributes is said to have a relation of degree 3. Chapter 1: Database Concepts Bob Dalesio and Philip Stanley. 1.6 A type is a named set of values. So the DBMS “protects users from the data” (i.e., it protects users from the details of how the data is physically represented inside the system). Learn vocabulary, terms, and more with flashcards, games, and other study tools. I’ve therefore decided to use both forms in this book, letting context be my guide in any given situation (and I won’t pretend I’ve been all that consistent in this regard, either). But as I’ve written elsewhere, I believe using the same example in a variety of different publications can be a help, not a hindrance, in learning. Different application programmers and various end-users have different views upon data, which must be derived from a common overall data structure. Literals: A literal is a “self-defining symbol”—i.e., it’s a symbol that denotes a value, and the value in question, and hence the type of that value also, are fixed and determined by the symbol in question (and are therefore known at compile time, incidentally). Database concepts (1) Robin Beaumont 14/09/2011 e-mail: robin@organplayers.co.uk D:\web_sites_mine\HIcourseweb new\chap7\s2\dbcon1.doc Page 6 of 12 In Access97 you can inspect the meta data that is stored about the current database you have open by clicking on the Tools menu -> Options ->View tab. Equality: The comparison v1 = v2 must give TRUE if and only if v1 and v2 are the very same value (implying, incidentally, that they must certainly be of the same type). Degree: The number of attributes in a relation determines the degree of relation. To be specific: In the case of variables, parameters, and read-only operators, the type in question is specified when the construct in question is defined. quiz which has been attempted 5340 times by avid quiz takers. (Actually they’re relations, as we’ll see in Chapter 2, but for the purposes of this introductory chapter “files” or “tables” will do.) So what I plan to do in this book is this: First, I’ll explain the relational model without using SQL at all (that’s Part I of the book). A relation has the following properties: Tuple: The rows of tables in a relationship are generally termed as Tuples. For further explanation of this point, see Chapter 2. For example, in the case of type INTEGER, which for simplicity I take to be system defined, the agency responsible for defining the type—in other words, the system, by my assumption—must define: Operators “:=”, “=”, “<”, etc., for assigning and comparing integers, Operators “+”, “*”, etc., for performing arithmetic on integers, Perhaps a CAST operator, for converting integers to character strings, But not character string operators such as “| |” (“concatenate”), SUBSTR (“substring”), etc., because—let’s agree, for the sake of the example at least—these operators make no sense for integers. See the answer to Q: at the end of the chapter. RDBMS is the basis for SQL, and for all modern database systems like MS SQL Server, IBM DB2, Oracle, MyS The column of a relation are assigned distinct names, and the ordering of these columns is immaterial. Users can insert new information into the database, and delete, change, or retrieve existing information in the database, by issuing requests or commands to the software that manages the database—which is to say, the database management system (DBMS for short). Airlines: reservations, schedules Telecommunication: records of calls, texts, and data usage, generating monthly bills, maintaining balances on prepaid calling cards Module-1: Database system concepts and Architecture • Centralized / Client-server Architecture for DBMS • Classification of DBMS Definition • A database management system (DBMS) is a collection of programs that enables users to create and maintain a database. Note in particular that literals and variable references are both expressions, since they certainly both denote values. What is OLTP? Part 1: Database Concepts Imagine that a countryside inn maintains its data in flat files on a file system. Integrity can be managed using the database. [4] By the way, that physical database, although it’s less abstract than the logical database, is still an abstraction; it consists, typically, of things like stored files and indexes, and those stored files and indexes are represented in terms of various lower level constructs such as pages and disk spaces. Database interrogation involves using the database management software to query (search) the database for information. Consider the code fragment shown in Figure 1-3. The code fragment in Figure 1-3 contains four assignment statements. The database is implemented through three general levels. Note: In the rest of this book I’ll abbreviate “suppliers under contract,” most of the time, to just suppliers. For example, the expression 2 + 3 is of type INTEGER, because the result 5 of evaluating that expression is of type INTEGER. Statements: The code overall consists of nine statements. International Islamic University See also www.thethirdmanifesto.com. Also, the chapter introduces the running example, which you’ll definitely need to be familiar with when we get to those later chapters. Their methods of searching and accessing of data will be different. Note: Security is important, of course, but further details of security controls are mostly beyond the scope of this book (except for a brief mention in Chapter 7). Also, there’s at most one shipment at any given time for a given supplier and given part, and so the combination of supplier number and part number is unique to any given shipment. Parts with weight less than 12.5. Note: The first two exercises in particular are slightly unfair, because I haven’t yet told you enough to answer them properly—but I think you should have a go at them anyway. The use of Databases can ensure data security. Finally, the reason for rehearsing all of this extremely familiar material is that (as I hope you were expecting) all of the foregoing concepts are directly relevant to databases, as we’ll see in the chapters to come. Unfortunately, it has become common in the database field—I’m tempted to say, extremely common—to use the term database to mean a DBMS! Of course, it isn’t possible to set any particularly searching exercises at this early point in the book, and the following are little more than review questions. Now, a standard concrete language does exist: viz., SQL (pronounced “ess cue ell,” or sometimes “sequel”), which is supported, more or less, by all of the mainstream database products on the market today. But the relational model doesn’t prescribe any such language; that is, it doesn’t prescribe a concrete syntax for how its concepts are to be realized in practice. In other words, the relational model can be thought of as a kind of recipe for what the user interface is supposed to look like in such a DBMS. It describes only part of databases. Try this amazing Database Concepts Exam Quiz: Trivia! Posted on October 11, 2017 February 14, 2020 by Ian. Since the database keeps on growing, then there may be frequent changes at times. One immediate and significant implication of the foregoing is this: Assuming the optimizer makes a reasonably good job of things, users shouldn’t have to get involved in performance issues at all. A database intends to have a collection of data stored together to serve multiple applications as possible. It’s also important to understand that the set of operators associated with any given type T must include both assignment (“:=”) and equality comparison (“=”). It follows that every variable, every parameter to every operator, every read-only operator, and every expression—in particular, every literal and every variable reference—is of some type as well, because all of these constructs, when they’re used, certainly do denote values. Note the following important corollary: If there exists some operator Op such that Op(v1) ≠ Op(v2), then v1 = v2 must give FALSE. Database minimizes data redundancy to a great extent. Current price $22.99. DataBase Concepts, Inc. specializes in software products and services for the petroleum industry. Table P represents kinds of parts. Hence a database is often conceived of as a repository of information needed for running certain functions in a corporation or organization. Now it’s your turn. Here’s a simple example: This expression—which of course represents the query “Get suppliers in London”—is making use of the relational restriction operator; formally, it’s asking for the set of suppliers represented in table S to be restricted to just the ones in London. Now, in practice, those user requests to the DBMS can be formulated in a variety of different ways (e.g., by pointing and clicking with a mouse). It’s deliberately not deep, and if you do already know something about database management you probably won’t find anything here you don’t already know. Attributes: The columns or fields of a table is termed as Attributes. Thus, the DBMS is responsible for (a) accepting user requests, be they queries or updates, that are expressed in terms of the logical database and (b) responding to those requests by interpreting and implementing them, or in other words executing them, in terms of the physical database. It was late in 1968 that Codd, a mathematician by training, first realized that the discipline of mathematics could be used to inject some solid principles and rigor into a field, database management, that prior to that time was all too deficient in any such qualities. A database is a structured collection of information on a defined subject. Oracle Corporation and its affiliates are not responsible for and expressly disclaim all warranties of any kind with respect to third-party content, products, and services unless otherwise set forth in an applicable agreement between you and Oracle. From everything I’ve said so far, it should be quite clear that there’s a logical difference between a database, which is a repository for data, and a DBMS, which is the software that manages such a repository. Examples throughout the rest of this book are based for the most part on the foregoing database. Suppose you were to ask the database whether there were any shipments for supplier S1 and, on receiving an answer in the affirmative, went on to ask what the average quantity was for those shipments; it would be very annoying (to say the least) to then be told there weren’t any such shipments after all—presumably because some other user had just deleted them. A statement in a programming language is a construct that causes some action to occur, such as defining or updating a variable or changing the flow of control. In fact, of course, such operators are in fact read-only operators; they’re just a special case, in which the type of the result they return is BOOLEAN. But the concepts the terminology refers to are actually quite simple (after all, the suppliers-and-parts database was pretty easy to understand, wasn’t it?). This should not lead to redesigning and re-implementation of the database. The purpose of that code fragment—which is expressed in a hypothetical but self-explanatory language—is to compute and display the sum of the integers in a certain one-dimensional array called A. Given a human resources database, for example, we might write: And this expression represents (let’s agree) a retrieval request—more usually known as a query—for employee information for employees whose job title is ‘Programmer’. Let me say too that even if it is somewhat unrealistic, the suppliers-and-parts database has at least been very carefully tailored to illustrate all kinds of points that we need to be examining later on; thus, it’s more than adequate for our purposes in this book. This part of the exercise was definitely unfair, but you probably guessed the answer anyway—just as restriction picks out certain rows, so the operation of projection, illustrated by this example, picks out certain columns. OLTP (Online Transactional Processing) is a category of data processing that is focused on transaction-oriented tasks. [8] Tutorial D has been revised and extended somewhat since that book was first published. a list of students with nut allergies, products from a particular supplier, etc. Refer to Figure 1-2. Next, I’ve said that every value is of some type. Certainly, you need a software to store, access, manage and update data. In order to illustrate the concepts I’m going to be discussing, I obviously need to show coding examples; thus, I clearly need some formal language in which to express those examples. Information versus Data The concepts of data independence prove beneficial in such types of contexts. Sync all your devices and never lose your place. I need to say a little more about the concept of types in particular. Tutorial D is a language expressly designed for use in illustrating relational concepts; prototype implementations do exist—see the website www.thethirdmanifesto.com—but, at the time of writing, no commercial products. © 2020, O’Reilly Media, Inc. All trademarks and registered trademarks appearing on oreilly.com are the property of their respective owners. It’s not so important to remember the actual data values in detail—though it certainly wouldn’t hurt if you did. To elaborate briefly: Security controls are needed to ensure that user requests are legitimate, in the sense that the user in question is requesting an operation he or she is allowed to carry out on data he or she is allowed to access. To repeat, then, a relational DBMS is a DBMS that supports a user interface that’s a faithful implementation of the relational model—meaning, as far as the user is concerned, that: Relational operators (i.e., operators that operate on data in relational form) are available to serve as a basis for formulating retrieval and update requests. Integrity controls protect the database from authorized but invalid operations. The rows in a table are called records and the columns in a table are called fields or attributes. [2] But still a computer professional, not a genuine “end user,” who might reasonably be quite ignorant of most of the matters to be discussed in this book. 1.3 A database is a repository for data stored electronically (an “electronic filing cabinet”). Comparison operators: A comparison operator is an operator like “<” that, when it’s invoked, returns a truth value (either TRUE or FALSE). As for the INSERT and DELETE operators, however, where no ambiguity arises, it can be a little tedious always to set them in all caps—especially when they’re being used as qualifiers, as in, e.g., “INSERT statement” (“insert statement”?). However, to the user who merely uses them (as opposed to the user who actually defines them), these user defined types will look exactly like system defined types anyway—indeed, that’s the whole point (or a large part of the point, at any rate). A description of the revised version (which is essentially the version I’ll be using in this book) can be found in another book by Hugh Darwen and myself, Database Explorations: Essays on The Third Manifesto and Related Topics (Trafford, 2010). Finally, let me say again that the reason for rehearsing all of this extremely familiar material is that once more (as I hope you were expecting) all of these concepts are directly relevant to databases, as we’ll see in the chapters to come. [3] I remind you from the preface that throughout this book I use “SQL and Relational Theory” as an abbreviated form of reference to my book SQL and Relational Theory: How to Write Accurate SQL Code (2nd edition, O’Reilly, 2012). But what’s a relational DBMS? Part number, color, and city for every part. The RuneScape Documentary - 15 Years of Adventure - Duration: 1… In this first part of the book, then, we’ll take a closer look at exactly what it means for data to “look relational,” and we’ll examine various relational operators and see how they can be used in practice. one-to-one (1:1 or 1..1) relationship associations among two or more entities that are used by data models. This is why IT companies have developed their database software products called as DBMS (D ata b ase M anagement S ystem). Likewise, an attempt to update the status for supplier S1 to 200 must also be rejected, if status values are supposed never to exceed 100. As the database may be viewed through three levels of abstraction, any change at any level can affect other levels' schemas. Now, you might well have seen this database before—I’ve used it in several other books and writings, including SQL and Relational Theory in particular,[3] as well as in numerous live presentations—and you might be forgiven for getting a little tired of it. RG Edu 91,401 views. To assist in reserving rooms and booking guests, the innkeepers use a custom application that accesses these flat files. So little or no generality is lost if, in my examples later in this book, I limit myself to system defined types such as INTEGER and CHAR (see below), and so I will, most if not quite all of the time. Recovery controls protect against data loss. 1.3 A database is a repository for data stored electronically (an “electronic filing cabinet”). One last point to close this section: You might or might not know (but I hope you do) that the relational model was originally the invention of E. F. Codd, when he was employed as a researcher at IBM (E for Edgar and F for Frank—but he always signed with his initials; to his friends, among whom I was proud to count myself, he was Ted). View 1 - database concepts.pdf from INFO 1103 at International Islamic University Malaysia (IIUM). Concurrency controls protect user operations from interfering with one another. Textbook Authors: Kroenke, David; Auer, David;, ISBN-10: 0133544621, ISBN-13: … EXTERNAL LEVEL OR VIEW LEVEL It defines a number of simplified domain-specific views. [6] I do not follow that usage in this book. Figure 1-1 below shows sample values for a typical database, having to do with suppliers, parts, and shipments (of parts by suppliers). Note: The operators INSERT, DELETE, and UPDATE mentioned in the answer to Q: are all relational update operators, and are thus by definition all effectively relational assignments. Of course, there are exactly two such values, denoted by the literals TRUE and FALSE. A Microsoft Access database is made up of several components, including: The ordering of rows in a relationship is immaterial. For example, in a geometric application, we might have user defined types called POINT, LINE, RECTANGLE, CIRCLE, and so on. Introduction to Basic Database Concepts Learn the basic fundamentals of databases Rating: 4.3 out of 5 4.3 (131 ratings) 1,299 students Created by Bluelime Learning Solutions. Welcome to the home page of Database System Concepts, Sixth Edition. 1.1 What do you think the following Tutorial D expressions represent? Physical data independence 2. But second, it’s also relational, which means the user interface is based on—better: is a faithful implementation of—the relational model. Database is a repository of organized collection of data such that data can be easily stored, maintained and retrieved. That logical database is contrasted with the corresponding physical database, which is the database as perceived by the DBMS (i.e., it’s the database as physically stored inside the computer system). 1.5 SQL is the standard language for interacting with “relational” databases; it’s supported by just about every mainstream database product on the market today. Please note, therefore, that in examples throughout the rest of this book, I’ll be assuming the specific sample values shown in Figure 1-1, barring explicit statements to the contrary. Second, I’ll show how ideas from the relational model are realized in concrete form in SQL specifically (that’s Part III of the book). Note carefully that a read-only operator, when it’s invoked, returns a result but doesn’t update anything (in particular, it doesn’t update its operands). Logical data independence Surely, if you want to claim that Technology A is no good and needs to be replaced by Technology B, then it’s incumbent on you to understand Technology A in the first place? Moreover, those different ways will typically have widely differing performance characteristics; in particular, they could have execution times that vary, quite literally, from fractions of a second to many days. Note: This requirement is sometimes referred to as The Assignment Principle. Concurrency controls have to do with the possibility that several users might be using the database at the same time. A DBMS is a software system that manages databases and access to those databases. Database Concepts answers to Chapter 4 - Data Modeling and the Entity-Relationship Model - Review Questions - Page 280 4.1 including work step by step written by community members like you. An update operator is an operator that updates some variable; in other words, it’s an assignment, logically speaking. The code fragment in Figure 1-3 involves four variables: I, N, SUM, and A. Nevertheless, I’d like to recommend that you try to answer them yourself before going on to read my answers in the next section. This software or hardware and documentation may provide access to or information about content, products, and services from third parties. As that figure is meant to suggest, the DBMS—the software that manages the database—effectively serves as a kind of intermediary between the logical and physical levels of the system: User requests for access to the database are expressed in terms of the logical database, and they’re implemented by the DBMS (“executed”) in terms of the corresponding physical database. Database is a collection of related data and data is a collection of facts and figures that can be processed to produce information.Mostly data represents recordable facts. [9] In fact, of exactly one type, unless type inheritance is a consideration, which in this book it isn’t. Now, the reason we might want to change the way the database is physically stored and accessed is almost always performance; and the fact that we can make such changes without having to change the way the database looks to the user means that existing application programs, queries, and the like can all still work after the change. There are many reasons why users may wish to query data, including: To identify a group of records that share a certain attribute – e.g. It follows that, logically speaking, assignment is the only update operator we need. By the way, notice the use of the keyword UPDATE (in upper case) in this exercise. Thus, it’s very important that the optimizer choose a “good” way to implement any given request, where “good” essentially means having good performance. Get Relational Theory for Computer Professionals now with O’Reilly online learning. Note: It follows that types are disjoint (at least as far as we’re concerned)—no value is of two or more types. Database 1 2010 24.99 978-0- 300 DB- Teaches you Fundamentals 98662 A02 the 83-1-1 fundamentals of databases Getting started 1 2010 24.99 978-0- 280 DB- Teaches you with DB2 98662 A01 the essentials Express-C 83-5-1 of DB2 using DB2 Express-C, the free version of DB2 Table: Book One general function provided by the DBMS is thus the shielding of users from details of the physical level of the system (very much as programming language systems also shield users from details of the physical level of the system). There’s one last thing I need to say regarding DBMSs in general. This document introduces concepts, principles, terminology, and architecture of near-zero downtime database migration for cloud architects who are migrating databases to Google Cloud from on-premises or other cloud environments. Assignment: Assignment (denoted “:=” in Figure 1-3) is an operator for updating a variable—that is, assigning a value, probably different from the previous value, to the variable in question. They’re meant to be understood as follows: Table S represents suppliers under contract. 1.4 Security controls protect the database from unauthorized operations. [9] The code fragment in Figure 1-3 involves three types: INTEGER (the set of all integers); ARRAY [1..N] OF INTEGER (the set of all one-dimensional arrays of integers with lower bound 1 and upper bound N); and CHAR (the set of all character strings). The point is this: Most requests (indeed, very likely all requests) are capable of being implemented in a variety—typically a very large variety—of different ways. (Easier for the system too, in certain respects; but the emphasis is on the user.) Data aids in producing information, which is based on facts. (As fort Part II, a brief explanation of what that’s about can be found in the preface.) Assignment 2: Database Concepts Part 1: MS Access The following ERD shows the entities included in a database system along with their relationships. The optimizer is the DBMS component that’s responsible for deciding exactly how to implement user requests. [7] Much simpler too than their counterparts in the various proposals—which crop up all too frequently, I’m sorry to say—for replacing the relational model (see, e.g., XML, NoSQL, the Actor Model, and on and on). Note too that every value effectively carries its type around with it. Third and last, it’s important to understand that associated with any given type T, there’s a set of operators defined for operating on values and variables of type T (because types without operators are useless). 1. [10] Note too that an expression, which I said earlier was a rule for computing a value, can equivalently be said to represent an invocation of some read-only operator; in fact, the terms expression and read-only operator invocation are effectively interchangeable. SQL - RDBMS Concepts - RDBMS stands for Relational Database Management System. As noted in the preface, however, SQL is very deeply flawed: It’s complex, incomplete, hard to learn, and indeed actively misleading in numerous ways. Database Concepts 1. Perhaps a little confusingly, it has become standard practice in the database world to use the uppercase term UPDATE to refer to the specific operator that changes existing data (as opposed to DELETE, which deletes existing data, and INSERT, which inserts new data), and the lowercase term update to refer to the INSERT, DELETE, and UPDATE operators considered generically. Database System Concepts Sixth Edition Avi Silberschatz Henry F. Korth S. Sudarshan McGraw-Hill ISBN 0-07-352332-1 Face The Real World of Database Systems Fully Equipped. In this book, therefore, when I want to refer to the UPDATE operator as such, I’ll set it in upper case (“all caps”) as just shown. In fact, it seems to me that the concepts in question are much simpler than their counterparts were in older, prerelational (and nonrelational) systems such as IMS and IDMS.[7]. Each shipment has one supplier number (SNO); one part number (PNO); and one quantity (QTY). Database programs are created using a program like Microsoft Access 2003. Contains only one table is called a flat database study tools on oreilly.com are the of. Called records and the columns or fields of a table are called fields or attributes so to. Three—And it can ’ t individual constant ” —e.g., the VAR statements—in Figure involves! And/Or deleting small amounts of data stored together to serve multiple applications as possible,... Continuous modification of data, generally stored and accessed electronically from a particular Group users! An operator that ( usually ) takes two values as operands and returns a value ( different values different... 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