DOCSLIB.ORG

Natural Versus Surrogate Keys. Performance and Usability

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Natural Versus Surrogate Keys. Performance and Usability Database Systems Journal vol. II, no. 2/2011 55 Natural versus Surrogate Keys. Performance and Usability Dragos-Paul POP Academy of Economic Studies, Bucharest, ROMANIA [email protected] Choosing the primary key for a table proves to be one of the most important steps in database design. But what happens when we have to pick between a natural or a surrogate key? Is there any performance issue that we must have in mind? Does the literature have a preferred pick? Is usability a concern? We’ll have a look at the advantages and disadvantages of both natural and surrogate keys and the performance and usability issues they address. Keywords: primary keys, natural keys, surrogate keys, superkey, candidate key, unique key, performance, usability. Introduction sometimes called a minimal superkey, 1 Choosing a primary key is really because a candidate key is, in fact, a important because it affects the database minimal set of attributes necessary to at the performance and usability levels. uniquely identify a tuple. In other words, a The literature speaks of both natural and set of attributes is said to be a candidate key surrogate keys and gives reasons for if there are no two tuples with the same choosing one over the other. value for the key and there is no other subset Before we get to talk about natural and of these attributes that can form a candidate surrogate keys in a relational key. This is where the “minimal” property of transactional table, we must define a few the candidate key derives from. A table can other key concepts used in the relational have multiple candidate keys. database model architecture. The Another concept related to the superkey is concepts to be defined are the superkey, the unique key. Again, just like a superkey the candidate key, the unique key and the and a candidate key, the unique key can primary key. uniquely identify each row in a table. 2 Key concepts Although this is not a rule, unique keys tend The superkey is defined as being a set of to only comprise a single column. The attributes of a given table that verifies difference between candidate keys and one main condition. The condition in unique keys is that, in practice, unique keys question is that there are no two distinct do not enforce the NOT NULL constraint. tuples in that table with an identical value This means they can contain the NULL for the superkey set. Also, the attributes value and still uniquely identify table rows. comprising the superkey set are said to be Why? Because of the way NULL is treated functionally dependent. This makes true by the database management systems. the following statement: if S is a NULL is not a value, but the absence of a superkey for the relation R, than the value, so the unique key concept holds true cardinality of the projection of R over S even for rows with NULL for the unique is the same as the cardinality of R. After key. This is because identification of two a table has gone through normalization, equal keys is done based on their values, and we can say that all its attributes form a since NULL is not a value, two keys superkey, because there are no two tuples containing NULL are not considered to be that are identical for all the values of the equal. This is by no means to be taken as a set. rule, because it differs in implementation From the superkey concept, we can across database management systems. A define the candidate key. This is better definition of a unique key is that two 56 Natural Versus Surrogate Keys. Performance and Usability tuples cannot have the same value for the record in a table. But this is where the unique key if NULL values are not used. similarity stops. They are keys that don’t So, a unique key only uniquely identifies have a natural relationship with the rest of rows that contain a value other than the columns in a table. The surrogate key is NULL for the key. As for the candidate just a value that is generated and then stored key, a table can have multiple unique with the rest of the columns in a record. The keys. key value is typically generated at run time The primary key is probably the most right before the record is inserted into a important concept in database design. A table. It is sometimes also referred to as a primary key is, basically, one of the dumb key, because there is no meaning candidate keys in a table. It is a unique associated with the value. Surrogate keys key that does not contain (and never will) are commonly a numeric number. NULL values can also be made a primary An important distinction between a key. For some tables, even a superkey surrogate and a primary key depends on can be a primary key (but that is a little whether the database is a current database or odd). So how and why is a primary key a temporal database. Since a current different form all the others? A table can database stores only currently valid data, only have one primary key and this key is there is a one-to-one correspondence the preferred way of identifying between a surrogate in the modeled world individual tuples. and the primary key of some object in the 3 Natural and surrogate keys database. In this case the surrogate may be Choosing the primary key has proven to used as a primary key, resulting in the term be the difficult part in database design. surrogate key. In a temporal database, This is because there are two types of however, there is a many-to-one relationship primary keys: natural and surrogate. between primary keys and the surrogate. The natural key, also called a domain key Since there may be several objects in the or an intelligent key, is a candidate key database corresponding to a single surrogate, that is logically related to the table. That we cannot use the surrogate as a primary is, it has business meaning, or business key; another attribute is required, in addition value. It is something that can be found in to the surrogate, to uniquely identify each nature, it makes sense. object. A natural key is a single column or set of Authors have argued that a surrogate should columns that uniquely identifies a single have the following characteristics: record in a table, where the key columns • the value is unique system‐wide, are made up of real data. When I say hence never reused “real data” I mean data that has meaning • the value is system generated and occurs naturally in the world of data. • the value is not modifiable by the user A natural key is a column value that has a or application relationship with the rest of the column • the value contains no semantic values in a given data record. Here are some examples of natural keys values: meaning Social Security Number, ISBN, and • the value is not visible to the user or TaxId. application On the other hand, the surrogate key is • the value is not composed of several not derived from real data; it does not values from different domains have any business meaning or logic. It is In practice, the surrogate key is frequently a a key most often generated by the number generated by the database database or made up using an algorithm. management system. For example, Oracle A surrogate key like a natural key is a uses sequences to accomplish this task, column that uniquely identifies a single while SQL server gives the “identity Database Systems Journal vol. II, no. 2/2011 57 column” option. PostgreSQL users have that are created from a hash of the ID the “serial” option, and MySQL ones use of your Ethernet card, or an an auto_increment attribute. Having the equivalent software representation, key independent of all other columns and the current datetime of your insulates the database relationships from computer system. The algorithm for changes in data values or database design doing this is defined by the Open (making the database more agile) and Software Foundation guarantees uniqueness. (www.opengroup.org). 4 Surrogate Key Implementation • Strategies Globally unique identifiers (GUIDs). There are several common options for GUIDs are a Microsoft standard that implementing surrogate keys: extend UUIDs, following the same • Key values assigned by the strategy if an Ethernet card exists and database. Most of the leading if not then they hash a software ID database vendors – companies and the current datetime to produce a such as Oracle, Microsoft and IBM value that is guaranteed unique to the – implement a surrogate key machine that creates it. strategy called incremental keys. • High‐low strategy. The basic idea is The basic idea is that they maintain that your key value, often called a a counter within the database persistent object identifier (POID) or server, writing the current value to simply an object identified (OID), is in a hidden system table to maintain two logical parts: A unique HIGH value consistency, which they use to that you obtain from a defined source assign a value to newly created and an N‐digit LOW value that your table rows. Every time a row is application assigns itself. Each time created the counter is incremented that a HIGH value is obtained the LOW and that value is assigned as the value will be set to zero. For example, key value for that row.
Load more

Recommended publications
  • Genesys Info Mart Physical Data Model for an Oracle Database
    Genesys Info Mart Physical Data Model for an Oracle Database Table RESOURCE_STATE_REASON 9/24/2021 Table RESOURCE_STATE_REASON Table RESOURCE_STATE_REASON Description Modified: 8.5.014.34 (in Microsoft SQL Server, data type for the following columns modified in single- language databases: REASON_TYPE, REASON_TYPE_CODE, HARDWARE_REASON, SOFTWARE_REASON_KEY, SOFTWARE_REASON_VALUE, WORKMODE, WORKMODE_CODE); 8.5.003 (in Oracle, fields with VARCHAR data types use explicit CHAR character-length semantics) In partitioned databases, this table is not partitioned. This table allows facts to be described by the state reason of the associated agent resource at a particular DN resource. Each row describes a hardware or software reason and a work mode. Tip To assist you in preparing supplementary documentation, click the following link to download a comma-separated text file containing information such as the data types and descriptions for all columns in this table: Download a CSV file. Hint: For easiest viewing, open the downloaded CSV file in Excel and adjust settings for column widths, text wrapping, and so on as desired. Depending on your browser and other system settings, you might need to save the file to your desktop first. Column List Legend Column Data Type P M F DV RESOURCE_STATE_REASON_KEYNUMBER(10) X X TENANT_KEY NUMBER(10) X X Genesys Info Mart Physical Data Model for an Oracle Database 2 Table RESOURCE_STATE_REASON Column Data Type P M F DV CREATE_AUDIT_KEYNUMBER(19) X X UPDATE_AUDIT_KEYNUMBER(19) X X VARCHAR2(64 REASON_TYPE CHAR) VARCHAR2(32 REASON_TYPE_CODE CHAR) VARCHAR2(255 HARDWARE_REASON CHAR) VARCHAR2(255 SOFTWARE_REASON_KEY CHAR) VARCHAR2(255 SOFTWARE_REASON_VALUE CHAR) VARCHAR2(64 WORKMODE CHAR) VARCHAR2(32 WORKMODE_CODE CHAR) PURGE_FLAG NUMBER(1) RESOURCE_STATE_REASON_KEY The primary key of this table and the surrogate key that is used to join this dimension to the fact tables.
    [Show full text]
  • Create Table Identity Primary Key Sql Server
    Create Table Identity Primary Key Sql Server Maurits foozle her Novokuznetsk sleeplessly, Johannine and preludial. High-principled and consonantal Keil often stroke triboluminescentsome proletarianization or spotlight nor'-east plop. or volunteer jealously. Foul-spoken Fabio always outstrips his kursaals if Davidson is There arise two ways to create tables in your Microsoft SQL database. Microsoft SQL Server has built-in an identity column fields which. An identity column contains a known numeric input for a row now the table. SOLVED Can select remove Identity from a primary case with. There cannot create table created on every case, primary key creates the server identity column if the current sql? As I today to refute these records into a U-SQL table review I am create a U-SQL database. Clustering option requires separate table created sequence generator always use sql server tables have to the key. This key creates the primary keys per the approach is. We love create Auto increment columns in oracle by using IDENTITY. PostgreSQL Identity Column PostgreSQL Tutorial. Oracle Identity Column A self-by-self Guide with Examples. Constraints that table created several keys means you can promote a primary. Not logged in Talk Contributions Create account already in. Primary keys are created, request was already creates a low due to do not complete this. IDENTITYNOT NULLPRIMARY KEY Identity Sequence. How weak I Reseed a SQL Server identity column TechRepublic. Hi You can use one query eg Hide Copy Code Create table tblEmplooyee Recordid bigint Primary key identity. SQL CREATE TABLE Statement Tutorial Republic. Hcl will assume we need be simplified to get the primary key multiple related two dissimilar objects or adding it separates structure is involved before you create identity? When the identity column is part of physician primary key SQL Server.
    [Show full text]
  • Alter Table Column Auto Increment Sql Server
    Alter Table Column Auto Increment Sql Server Esau never parchmentize any jolters plenish obsequiously, is Brant problematic and cankered enough? Zacharie forespeaks bifariously while qualitative Darcy tumefy availingly or meseems indisputably. Stolidity Antonino never reawakes so rifely or bejeweled any viol disbelievingly. Cookies: This site uses cookies. In sql server table without the alter table becomes a redbook, the value as we used. Change it alter table sql server tables have heavily used to increment columns, these additional space is structured and. As a result, had this name changed, which causes data layer in this column. Each path should be defined as NULL or NOT NULL. The illustrative example, or the small addition, database and the problem with us improve performance, it gives the actual data in advanced option. MUST be some option here. You kill of course test the higher values as well. Been logged in sql? The optional column constraint name lets you could or drop individual constraints at that later time, affecting upholstery, inserts will continue without fail. Identity columns are sql server tables have data that this data type of rust early in identity. No customs to concern your primary key. If your car from making unnatural sounds or rocks to help halt, give us a call! Unexpected error when attempting to retrieve preview HTML. These faster than sql server table while alter local processing modes offered by the alter table column sql auto server sqlcmd and. Logged Recovery model to ensure minimal logging. We create use table to generate lists of different types of objects that reason then be used for reporting or find research.
    [Show full text]
  • Keys Are, As Their Name Suggests, a Key Part of a Relational Database
    The key is defined as the column or attribute of the database table. For example if a table has id, name and address as the column names then each one is known as the key for that table. We can also say that the table has 3 keys as id, name and address. The keys are also used to identify each record in the database table . Primary Key:- • Every database table should have one or more columns designated as the primary key . The value this key holds should be unique for each record in the database. For example, assume we have a table called Employees (SSN- social security No) that contains personnel information for every employee in our firm. We’ need to select an appropriate primary key that would uniquely identify each employee. Primary Key • The primary key must contain unique values, must never be null and uniquely identify each record in the table. • As an example, a student id might be a primary key in a student table, a department code in a table of all departments in an organisation. Unique Key • The UNIQUE constraint uniquely identifies each record in a database table. • Allows Null value. But only one Null value. • A table can have more than one UNIQUE Key Column[s] • A table can have multiple unique keys Differences between Primary Key and Unique Key: • Primary Key 1. A primary key cannot allow null (a primary key cannot be defined on columns that allow nulls). 2. Each table can have only one primary key. • Unique Key 1. A unique key can allow null (a unique key can be defined on columns that allow nulls.) 2.
    [Show full text]
  • Rfgen Users Guide
    DataMax Software Group Inc. 1101 Investment Blvd. El Dorado Hills, CA 95762 USA RFgen Users Guide All Editions RFgen 5.2 © 2021 RFgen Software. A division of DataMAX Software Group, Inc. All Rights Reserved. RFgen 5.2 Users Guide Table of Contents Introduction to RFgen 1 Connection Tab 33 Basic Implementation Steps 2 Connection Tab - SAP 33 Configuration Overview 3 SAP Data Encryption 34 Configurations Shared by Dev Studio To Configure for JDE 35 and Services Console: 3 Adding A New Web Services Connection 40 Connections Shared by Dev Studio Configuring the Host Connection 42 and Services Console: 4 Configuring User Access Control 45 Configurations Available Only in Dev Studio 4 Adding or Removing RFgen Admin- istrators / RFgen SubAdmins 46 Connections Available Only in Dev Studio 4 Dev Studio Configuration Options 47 Configuring the RFgen Application Data- Configuring Menu and Key Settings 48 base 4 System Menu Configuration 48 Configuring Application Preferences 7 Function Key Actions 49 Configuring Application Services 10 Configuring the Scripting Environment 50 Configuring Environment Settings 14 Configuring Source Control Options 52 Configure System Environment 14 Configuring System Properties 54 Configuring Transaction Management DB Connection 19 Download Enterprise Objects 54 Create Application Event Database 19 Downloading ERP Business Functions 55 Configuring System Queues and Tasks 20 Downloading JDE Processing Options 55 Add New Enterprise Connections 22 Viewing Enterprise Objects 57 Adding a New DataSource Connection 22 Viewing
    [Show full text]
  • CANDIDATE KEYS a Candidate Key of a Relation Schema R Is a Subset X
    CANDIDATEKEYS A candidate key of a relation schema R is a subset X of the attributes of R with the following twoproperties: 1. Every attribute is functionally dependent on X, i.e., X + =all attributes of R (also denoted as X + =R). 2. No proper subset of X has the property (1), i.e., X is minimal with respect to the property (1). A sub-key of R: asubset of a candidate key; a super-key:aset of attributes containing a candidate key. We also use the abbreviation CK to denote "candidate key". Let R(ABCDE) be a relation schema and consider the fol- lowing functional dependencies F = {AB → E, AD → B, B → C, C → D}. Since (AC)+ =ABCDE, A+ =A,and C+ =CD, we knowthat ACisacandidate key,both A and C are sub-keys, and ABC is a super-key.The only other candidate keysare AB and AD. Note that since nothing determines A, A is in every can- didate key. -2- Computing All Candidate Keys of a Relation R. Givenarelation schema R(A1, A2,..., An)and a set of functional dependencies F which hold true on R, howcan we compute all candidate keysofR? Since each candidate key must be a minimal subset Z of {A1,..., + An}such that Z =R,wehav e the following straightforward (and brute-force) algorithm: (1) Construct alist L consisting of all non-empty subsets of {A1, n − ..., An}(there are 2 1ofthem). These subsets are arranged in L in ascending order of the size of the subset: 〈 〉 ≤ We get L = Z1, Z2,..., Z2n−1 ,such that |Zi| |Zi+1|.
    [Show full text]
  • Attunity Compose 3.1 Release Notes - April 2017
    Attunity Compose 3.1 Release Notes - April 2017 Attunity Compose 3.1 introduces a number of features and enhancements, which are described in the following sections: Enhanced Missing References Support Surrogate Key Enhancement Support for Archiving Change Tables Support for Fact Table Updates Performance Improvements Support for NULL Overrides in the Data Warehouse Creation of Data Marts in Separate Schemas or Databases Post-Upgrade Procedures Resolved Issues Known Issues Attunity Ltd. Attunity Compose 3.1 Release Notes - April 2017 | Page 1 Enhanced Missing References Support In some cases, incoming data is dependent on or refers to other data. If the referenced data is missing for some reason, you either decide to add the data manually or continue on the assumption that the data will arrive before it is needed. From Compose 3.1, users can view missing references by clicking the View Missing References button in the Manage ETL Sets' Monitor tab or by switching the console to Monitor view and selecting the Missing References tab below the task list. Attunity Ltd. Attunity Compose 3.1 Release Notes - April 2017 | Page 2 Surrogate Key Enhancement Compose uses a surrogate key to associate a Hub table with its satellites. In the past, the column containing the surrogate key (ID) was of INT data type. This was an issue with entities containing over 2.1 billions records (which is the maximun permitted INT value). The issue was resolved by changing the column containing the surrogate key to BIGINT data type. Attunity Ltd. Attunity Compose 3.1 Release Notes - April 2017 | Page 3 Support for Archiving Change Tables From Compose 3.1, you can determine whether the Change Tables will be archived (and to where) or deleted after the changes have been applied.
    [Show full text]
  • There Are Only Four Types of Relational Keys Candidate Key As Stated
    There are only four types of relational keys Candidate Key As stated above, a candidate key is any set of one or more columns whose combined values are unique among all occurrences (i.e., tuples or rows). Since a null value is not guaranteed to be unique, no component of a candidate key is allowed to be null. There can be any number of candidate keys in a table . Relational pundits are not in agreement whether zero candidate keys is acceptable, since that would contradict the (debatable) requirement that there must be a primary key. Primary Key The primary key of any table is any candidate key of that table which the database designer arbitrarily designates as "primary". The primary key may be selected for convenience, comprehension, performance, or any other reasons. It is entirely proper (albeit often inconvenient) to change the selection of primary key to another candidate key. As we will see below, there is no property of a primary key which is not shared by all other candidate keys in of the table except this arbitrary designation. Unfortunately E-R methodologies and RDBMS products have come to rely on the primary key almost to the exclusion of the concept of candidate keys, which are rarely supported by software. Alternate Key The alternate key s of any table are simply those candidate keys which are not currently selected as the primary key. According to { Date95 } (page 115), "... exactly one of those candidate keys [is] chosen as the primary key [and] the remainder, if any, are then called alternate keys ." An alternate key is a function of all candidate keys minus the primary key.
    [Show full text]
  • Data Vault Data Modeling Specification V 2.0.2 Focused on the Data Model Components
    Data Vault Data Modeling Specification v2.0.2 Data Vault Data Modeling Specification v 2.0.2 Focused on the Data Model Components © Copyright Dan Linstedt, 2018 all rights reserved. Abstract New specifications for Data Vault 2.0 Methodology, Architecture, and Implementation are coming soon... For now, I've updated the modeling specification only to meet the needs of Data Vault 2.0. This document is a definitional document, and does not cover the implementation details or “how-to” best practices – for those, please refer to Data Vault Implementation Standards. Please note: ALL of these definitions are taught in our Certified Data Vault 2.0 Practitioner course. They are also defined in the book: Building a Scalable Data Warehouse with Data Vault 2.0 available on Amazon.com These standards are FREE to the general public, and these standards are up-to-date, and current. All standards published here should be considered the correct and current standards for Data Vault Data Modeling. NOTE: tooling vendors: if you *CLAIM* to support Data Vault 2.0, then you must support all standards as defined here. Otherwise, you are not allowed to claim support of Data Vault 2.0 in any way. In order to make the public statement “certified/Authorized to meet Data Vault 2.0 Standards” or “endorsed by Dan Linstedt” you must make prior arrangements directly with me. © Copyright Dan Linstedt 2018, all Rights Reserved Page 1 of 17 Data Vault Data Modeling Specification v2.0.2 Table of Contents Abstract .........................................................................................................................................1 1.0 Entity Type Definitions .............................................................................................................4 1.1 Hub Entity ......................................................................................................................................................
    [Show full text]
  • All Keys in Dbms with Example
    All Keys In Dbms With Example Leigh usually fudging whithersoever or concertina ineffably when diachronic Dickey unbuilds eventually and catachrestically. Nocturnal Chane toast deafly or syllabify presumptively when Dirk is gratulatory. Muriatic and strawy Pavel feds almost algebraically, though Rolfe evolve his almahs hobnails. We would make the keys in all dbms example of attributes Is known s control key contains a database choosing a set to retrieve the same plant as with all in dbms keys in below. Keys with all you can be in all dbms keys with example to? This example to all the ad links and in all dbms keys with example: the minimum number also update operation that each tuple. Used for each employee, let us in the. Nulls in your experience platforms are two same first columns as primary key are required for this set to table roll_no, as demonstrated here. It would work as the keys with the foreign. What is referred table then the curve with all keys in dbms example, you would be a list? Ssis tutorial of your dbms keys by the tables suggests that is not simple words, driving license number field cannot be ignored during your preferred and in all dbms keys with example. Solution for me with databases and with all keys in example, various levels table. You with all keys in dbms example, andere brauche ich für statistiken zu verfolgen. The following example: roll number of the keys and design stage, and with all candidate key in all dbms keys with example might be in.
    [Show full text]
  • 3 Data Definition Language (DDL)
    Database Foundations 6-3 Data Definition Language (DDL) Copyright © 2015, Oracle and/or its affiliates. All rights reserved. Roadmap You are here Data Transaction Introduction to Structured Data Definition Manipulation Control Oracle Query Language Language Language (TCL) Application Language (DDL) (DML) Express (SQL) Restricting Sorting Data Joining Tables Retrieving Data Using Using ORDER Using JOIN Data Using WHERE BY SELECT DFo 6-3 Copyright © 2015, Oracle and/or its affiliates. All rights reserved. 3 Data Definition Language (DDL) Objectives This lesson covers the following objectives: • Identify the steps needed to create database tables • Describe the purpose of the data definition language (DDL) • List the DDL operations needed to build and maintain a database's tables DFo 6-3 Copyright © 2015, Oracle and/or its affiliates. All rights reserved. 4 Data Definition Language (DDL) Database Objects Object Description Table Is the basic unit of storage; consists of rows View Logically represents subsets of data from one or more tables Sequence Generates numeric values Index Improves the performance of some queries Synonym Gives an alternative name to an object DFo 6-3 Copyright © 2015, Oracle and/or its affiliates. All rights reserved. 5 Data Definition Language (DDL) Naming Rules for Tables and Columns Table names and column names must: • Begin with a letter • Be 1–30 characters long • Contain only A–Z, a–z, 0–9, _, $, and # • Not duplicate the name of another object owned by the same user • Not be an Oracle server–reserved word DFo 6-3 Copyright © 2015, Oracle and/or its affiliates. All rights reserved. 6 Data Definition Language (DDL) CREATE TABLE Statement • To issue a CREATE TABLE statement, you must have: – The CREATE TABLE privilege – A storage area CREATE TABLE [schema.]table (column datatype [DEFAULT expr][, ...]); • Specify in the statement: – Table name – Column name, column data type, column size – Integrity constraints (optional) – Default values (optional) DFo 6-3 Copyright © 2015, Oracle and/or its affiliates.
    [Show full text]
  • CSC 443 – Database Management Systems Data and Its Structure
    CSC 443 – Database Management Systems Lecture 3 –The Relational Data Model Data and Its Structure • Data is actually stored as bits, but it is difficult to work with data at this level. • It is convenient to view data at different levels of abstraction . • Schema : Description of data at some abstraction level. Each level has its own schema. • We will be concerned with three schemas: physical , conceptual , and external . 1 Physical Data Level • Physical schema describes details of how data is stored: tracks, cylinders, indices etc. • Early applications worked at this level – explicitly dealt with details. • Problem: Routines were hard-coded to deal with physical representation. – Changes to data structure difficult to make. – Application code becomes complex since it must deal with details. – Rapid implementation of new features impossible. Conceptual Data Level • Hides details. – In the relational model, the conceptual schema presents data as a set of tables. • DBMS maps from conceptual to physical schema automatically. • Physical schema can be changed without changing application: – DBMS would change mapping from conceptual to physical transparently – This property is referred to as physical data independence 2 Conceptual Data Level (con’t) External Data Level • In the relational model, the external schema also presents data as a set of relations. • An external schema specifies a view of the data in terms of the conceptual level. It is tailored to the needs of a particular category of users. – Portions of stored data should not be seen by some users. • Students should not see their files in full. • Faculty should not see billing data. – Information that can be derived from stored data might be viewed as if it were stored.
    [Show full text]