Lecture 5 STRUCTURED ANALYSIS PB007 Software Engineering I Faculty of Informatics, Masaryk University Fall 2017 1© Bühnová, Sochor, Ráček Outline ² Yourdon Modern Structured Analysis (YMSA) § Context diagram (CD) § Data flow diagram (DFD) ² Data modelling § Entity relationship diagram (ERD) ² Relational database design § Normalization 2© Bühnová, Sochor, Ráček Yourdon Modern Structured Analysis (YMSA) Lecture 5/Part 1 3© Bühnová, Sochor, Ráček E. Yourdon: Modern structured analysis 4 Environment model Behavioral model Functional decomposition © Bühnová, Sochor, Ráček Events: E1: registered E2: rolled in E3: rolled out E4: started E5: ended Course Teacher Student Data model Environment model ² Context diagram is a special case of a data flow diagram, containing a single process representing the whole system. It emphasizes: § Terminators – people and systems communicating with the system § Data received from the environment that shall be processed § Data produced by the system and sent to the environment § Data stores shared by the system and its terminators § System boundary ² Event list is a textual list of stimuli coming from the environment that must be responded by the system. 5© Bühnová, Sochor, Ráček Context diagram example 6© Bühnová, Sochor, Ráček Customers orders, canceled orders BookProduction Accounting Management orders of extra prints books to store invoice sell report invoice, delivery note Book selling eshop Account balance Behavioral model ² Behavioral model specifies the flow of data through the modeled information system, modeling its process aspects. § It shows what kinds of information will be input to and output from the system, where the data will come from and go to, and where the data will be stored. § It does not show information about the timing of processes, or information about whether processes will operate in sequence or in parallel. ² Data flow diagram (DFD) is a graphical representation of the system as a network of processes that fulfill system functions and communicate through system data. 7© Bühnová, Sochor, Ráček Data flow diagram (DFD) ² DFD consists of four types of elements: § Processes § Data flows § Data stores § Terminators 8© Bühnová, Sochor, Ráček Account update Account Account verificationClient withdraw command authorized command account balance updated account transaction record Transactions archive Processes and Data flows ² A Process models a part of the system that transforms specific inputs to outputs. ² Name of a process is a single word, phrase or simple sentence, e.g. “User authentication”. § The process name sometimes contains the name of a person, group of people, department or device – specifying also the actor or tool of the process. ² A Data flow models a way for data transfer from one part of the system to another. § Flows can also model the transfer of physical materials. 9© Bühnová, Sochor, Ráček Data stores ² Data store models a static collection of data that are shared by two or more processes operating in different time. § Name is a plural of the data name going to and coming from the data store. 10© Bühnová, Sochor, Ráček Answer queries Orders Record order order order detail reply query order confirmation Terminators ² A Terminator represents an external entity communicating with the system. ² The flows connecting terminators with the processes or data stores inside the system represent the interfaces between the system and its environment. 11© Bühnová, Sochor, Ráček Account update Account Account verificationClient withdraw command authorized command account balance updated account transaction record Transactions archive Top-down and bottom-up DFD balancing 12 primary DFD 98 processes first balancing 14 processes system DFD 2 processes © Bühnová, Sochor, Ráček What are the disadvantages of the two approaches? Data modelling Lecture 5/Part 2 13© Bühnová, Sochor, Ráček Data modeling ² Defines static data structure, relationships and attributes ² Complementary to the behavior model in structured analysis; models information not covered by DFDs ² More stable and essential information comparing to DFD ² Entity-Relationship modeling § Identify system entities – both abstract (lecture) and concrete (student) § For each entity examine – the purpose of the entity, its constituents (attributes) and relationships among entities § Check model consistency and include data details 14© Bühnová, Sochor, Ráček Entity Relationship Diagram (ERD) ² Entities and their types ² Relationships and their types ² Attributes and their domains 15© Bühnová, Sochor, Ráček Chen's notation (concept level description) Teacher Lecturegives date length place name contact name 1 (1,1) N (0,8) Teacher Lecture (0,8) name contact name date length place (1,1) Crow’s Foot notation (implementation level descript.) gives Entities and Entity types ² An Entity is anything about which we want to store data § Identifiable – entities can be distinguished by their identity § Needed – has significant role in the designed system § Described by attributes shared by all entities of the same type ² An Entity set is a set of entities of the same Entity type. 16 Entity Entity type You Student Your neighbor Student Me Teacher This PB007 lecture Lecture Student Lecture Teacher © Bühnová, Sochor, Ráček Relationships and Relationship types ² Entities take part in Relationships (among possibly more than two entities), that can often be identified from verbs or verb phrases. § You are attending this PB007 lecture. § I am giving this PB007 lecture. ² A Relationship set is a set of relationships of the same Relationship type. § A student attends a lecture. § A teacher gives a lecture. 17 Student Lecture attends gives Teacher © Bühnová, Sochor, Ráček Attributes and Attribute domains ² An Attribute is a fact, aspect, property, or detail about either an entity type or a relationship type. § E.g. a lecture might have attributes: time, date, length, place. ² An Attribute type is a type domain of the attribute. If the domain is complex (domain of an attribute address), the attribute may be an entity type instead. 18 Lecture time date length place © Bühnová, Sochor, Ráček givesTeacher Attributes or entities? ² To decide whether a concept be modeled as an attribute or an entity type: § Do we wish to store any information about this concept (other than an identifying name)? § Is it single-valued? § E.g. objectives of a course – are they more than one? If just one, how complex information do we want to store about it? ² General guidelines: § Entities can have attributes but attributes have no smaller parts. § Entities can have relationships between them, but an attribute belongs to a single entity. 19© Bühnová, Sochor, Ráček Relationship-type degree 20 Every manager leads exactly one department. Every department is led by exactly one manager. Every edition plan contains one or more book titles. Every book title is part of exactly one edition plan. Every producer produces one or more products. Every product is produced by one or more producers. © Bühnová, Sochor, Ráček Manager leads Department 11 Edition plan contains Book title N1 Producer produces Product NM Relationship-type degree 21 Mandatory relationship Optional relationship Recursive relationship © Bühnová, Sochor, Ráček Painter drew Painting N1 Employee works on Project N (0,N) M (0,M) Module consists of 1 N Cardinality ratio ² Cardinality ratio of a relationship type describes the number of entities that can participate in the relationship. ² One to one 1:1 § Each lecturer has a unique office. ² One to many 1:N § A lecturer may tutor many students, but each student has just one tutor. ² Many to many M:N § Each student takes several modules, and each module is taken by several students. 22© Bühnová, Sochor, Ráček More relationships between two entities ² Relationship offers has attributes: § payment conditions, due date. ² Relationship delivered has attributes: § delivery note details. 23© Bühnová, Sochor, Ráček Product offers Supplier NM delivered NM Relationships among more than two entities 24© Bühnová, Sochor, Ráček Seller negotiate price Agent 11 Buyer’s lawyer negotiate conditions Seller’s lawyer NM Buyer 1 1 Association entity ² The Contract exists just as a result of the relationship between the Customer and Product entity. 25 association entity © Bühnová, Sochor, Ráček Customer buys Product NM Contract Super-type and sub-type entities ² Extended ERDs model also inheritance, i.e. the relationship of specialization–generalization 26 super-type entity sub-type entity © Bühnová, Sochor, Ráček Compact VanSUV Car ERD modeling in structured analysis ² Iterative development in structured analysis § Entities identification -> initial ERD § Attributes identification -> detailed ERD § Identification of missing and redundant entities • Entities constituting of only one attribute (identifier) • Entity sets consisting of a single entity • Derived entities and relationships • Association entities • ERD-DFD consistency and completeness checking ² Modeled in parallel with DFD 27© Bühnová, Sochor, Ráček Removal of unneeded (redundant) entities 28 The Spouse entity is better suited as Employee’s attribute. © Bühnová, Sochor, Ráček Employee married Spouse 1 1 Employee spouse Removal of unneeded (redundant) entities 29© Bühnová, Sochor, Ráček Patient receives Medicament NM Treatment Patient 1 Treatment receives N medicament Removal of unneeded relationships 30 The duty to renew the license can be derived from the entities © Bühnová, Sochor, Ráček Driver has License Driver License renews has Data dictionary ² Used for documentation of complex ERD models ² Symbols: § = consists of § + and § ( ) optional part (0 or 1) § [ | ] alternative choice § { } iteration (1 or more) a=1{b}15 § * * comment § @ identifier (key) 31© Bühnová, Sochor, Ráček Example – Order ² Order no. 2012-007-24 ² Issue date: 23.4.2012 Delivery date: 30.4.2012 ² Customer: no. 007 Dr. John Smith ² Goods: Number Name Pieces Price/piece P3876 Software engineering 6 135 H4681 UML2 and the UP 4 52 X6574 SA in practice 3 50 32© Bühnová, Sochor, Ráček Example – Order ² ORDER = @number + issue date + ( delivery date ) + customer number + customer name + { product number + product name + ordered pieces + ( product price per piece ) } ² customer name = ( title) + first name + surname ² title = [ Mr. | Mrs. | Miss. | Dr. | Prof. ] ² first name = { allowed symbol } ² allowed symbol = [ A - Z | a - z | ] 33© Bühnová, Ráček, Sochor Relational Database Design Lecture 5/Part 3 34© Bühnová, Sochor, Ráček Crow's Foot notation 35 Entity Entity Entity Entity Exactly one occurrence None or one occurrence One or more occurrence None or more occurrences © Bühnová, Sochor, Ráček relationship relationship relationship relationship ERD example – Transport 36© Bühnová, Sochor, Ráček Carrier Driver Journey License Vehicle employs takes part in is a holder of is assigned to ERD example – Library 37© Bühnová, Sochor, Ráček Reservation Book Copy Loan Reader is reserved is available is on loanhas entered ERD example – Book editing 38© Bühnová, Sochor, Ráček Handbook Chapter Author coauthored by reviewed byconsists of written by Relational database design based on ERDs ² Entity-relationship modeling is a first step towards database design. Database design process: 1. Determine the purpose of the database. 2. Find and organize the information required - Create ERD model of the system. Each entity type becomes a table, attribute becomes a column, entity becomes a row in the table. Handle relationships with attributes, association entities and M:N relationships. 39© Bühnová, Sochor, Ráček Relationships to entities 40© Bühnová, Sochor, Ráček Customer Product N1 Customer Product Purchase purchases Can the purchase entity be omitted? date Association entities 41 … can become an entity on its own Association entity… © Bühnová, Sochor, Ráček Customer Product NM Order Customer Product Order M:N relationships 42© Bühnová, Sochor, Ráček Teacher Course NM Teacher Course Teaching teaches Sub-types and super-types 43© Bühnová, Sochor, Ráček super-type entity sub-type entityCompact VanSUV Car ² Three options: § One big Car entity with all attributes § Three smaller Compact, SUV and Van entities § Four entities with relationship between sub-type and super-type entity Database design process (continued) 3. Specify primary keys - Choose each table’s primary key. The primary key is a column that is used to uniquely identify each row. An example might be Product ID or Order ID. 4. Apply the normalization rules - Apply the data normalization rules to see if tables are structured correctly. Make adjustments to the tables. 5. Refine the design - Analyze the design for errors. Create tables and add a few records of sample data. Check if results come from the tables as expected. Make adjustments to the design, as needed. 44© Bühnová, Sochor, Ráček Entities and keys ²Superkey § A set of attributes that uniquely identifies each entity. ² Candidate key § A non-redundant superkey, i.e. all items of a candidate key are necessary to identify an entity, no key attribute can be removed. § There can be more combinations of entity attributes that can be used as candidate keys. ² Primary key § The selected candidate key, marked with # symbol. ² Foreign key § A set of attributes in one entity that uniquely identifies (i.e. is a primary key in) another entity. 45© Bühnová, Sochor, Ráček Data normalization goals by E.F. Codd ² Minimize redundancy and dependency § Minimize redesign when extending database structure § Make the data model more informative to users ² Free the database of modification anomalies § Update anomaly – the same information expressed on multiple rows → update resulting in logical inconsistencies. § Insertion anomaly – certain facts cannot be recorded, because of their binding with another information into one record. § Deletion anomaly – deletion of data representing certain facts necessitating deletion of unrelated data. ² Avoid bias towards any particular pattern of querying 46© Bühnová, Sochor, Ráček 47 empl# name sex expert experience employee expertise empl# name sex 1. Normal form empl# expert# experience Def.1NF: A relation is in 1NF if the domain of each attribute contains only atomic values, and the value of each attribute contains only a single value from that domain. © Bühnová, Sochor, Ráček 1. Normal form – no repeating groups 48 1. Normal form – normalization example © Bühnová, Sochor, Ráček EntityA EntityB idA attribute1 attribute2 idB attribute3 EntityA idA attribute1 attribute2 attribute3[1] attribute3[2] attribute3[n] Functional dependency ² Functional dependency § In a given table, an attribute Y is said to have a functional dependency on a set of attributes X if and only if each X value is associated with precisely one Y value. ² Trivial functional dependency § A trivial functional dependency is a functional dependency of an attribute on a superset of itself. ² Full functional dependency § An attribute is fully functionally dependent on a set of attributes X if it is: functionally dependent on X, and not functionally dependent on any proper subset of X. 49© Bühnová, Sochor, Ráček X1 X2 … Y X1 X2 X1 X2 … Y 50 2. Normal form – no partial dependency empl# name salary project deadline developer# package# developer name package name hours Example EMPLOYEE Example PROGRAMING Is in 2NF Not in 2NF Def. 2NF: In 1NF and no non-prime attribute in the table is functionally dependent on a proper subset of any candidate key. © Bühnová, Sochor, Ráček What anomalies can you identify in this example? 51 2. Normal form – no partial dependency manufacturer model model full name# manufacturer country Example DISHWASHER MODELS Not in 2NF Def. 2NF: In 1NF and no non-prime attribute in the table is functionally dependent on a proper subset of any candidate key. • Does the “candidate key” part of the definition make difference? • When there is only one-item primary key, is 2NF guaranteed? © Bühnová, Sochor, Ráček not part of any candidate key 52 2. Normal form – normalization example course# student# student name student email registration date student# student name student email course# student# registration date © Bühnová, Sochor, Ráček 53 3. Normal form – no transitive dependency Def. 3NF: In 2NF and every non-prime attribute is non-transitively (i.e. only directly) dependent on every candidate key. © Bühnová, Sochor, Ráček What anomalies can you identify in this example? empl# name salary project deadline Example EMPLOYEE Not in 3NF 54 3. Normal form – normalization example deadline is transitively dependent on empl# © Bühnová, Sochor, Ráček empl# name salary project deadline empl# name salary project project# deadline ERD vs. UML Class Diagram 55 ² Class diagrams § model both structural and behavior features of a system (attribute and operations), § contain many different types of relationships (association, aggregation, composition, dependency, generalization), and § are more likely to map into real-world objects. ² Entity relationship models § model only structural data view with a low variety of relationships (simple relations and rarely generalization), and § are more likely to map into database tables (repetitive records). § They allow us to design primary and foreign entity keys, and used to be normalized to simplify data manipulation. © Bühnová, Sochor, Ráček ERD vs. UML Class Diagram 56 ² Although there can be one to one mapping between ERD and Class diagram, it is very common that § one class is mapped to more than one entity, or § more classes are mapped to a single entity. ² Furthermore, not all classes need to be persistent and hence reflected in the ERD model, which uses to be driven by the database design. ² Summary: § ERD is data-oriented and persistence-specific § Class diagram targets also operations and is persistence independent © Bühnová, Sochor, Ráček Key points ² Structured analysis, and YMSA in particular, models systems from the perspectives of: § system interaction with its environment (CD), and § hierarchy of system processes and data flows (DFD). ² Data modeling, and ERD in particular, focuses on modeling data entities, relationships and attributes. ² Data normalization focuses on reducing redundancy and dependency in database design, and on avoiding bias towards a particular pattern of querying. § 1NF: no repeating groups § 2NF: no partial dependency § 3NF: no transitive dependency 57© Bühnová, Ráček, Sochor