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CSCE 431: From Models to Implementation

CSCE 431: From Models to Implementation. Some material from Bruegge , Dutoit. Outline. From Object Model to Code Mapping models to code Operations on the object model: Optimizations to address performance requirements Implementation of class model components

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CSCE 431: From Models to Implementation

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  1. CSCE 431:From Models to Implementation Some material from Bruegge, Dutoit

  2. Outline • From Object Model to Code • Mapping models to code • Operations on the object model: • Optimizations to address performance requirements • Implementation of class model components • Realization of associations • Realization of operation contracts • From Object Model to Persistent Data • Summary CSCE 431 From Models to Implementation

  3. Development Activities • Improve modularity and performance • Transform associations into references, because programming languages do not support associations • Relations to functions • If the programming language does not support contracts, write code for detecting and handling contract violations (or leave as documentation) CSCE 431 From Models to Implementation

  4. Model-Driven Engineering (MDE) • Vision • Object model realizes the use case, which directly maps to implementation (model-driven engineering) • Maybe implementation even generated • Reality • Model and code out of sync • Examples: • A new parameter added to an operation, only added to the source code, but not to the object model • Additional attributes are added to an entity object, but the data base table is not updated (as a result, the new attributes are not persistent) CSCE 431 From Models to Implementation

  5. Object Model  Code; Issues • No direct language construct for UML associations • Transformed into collections of object references • Most languages do not support contracts (invariants, pre and post conditions) • Contracts manually transformed to error detection and handling code, asserts, etc. (or ignored) • If a model changes, effecting the same change in code is a manual process CSCE 431 From Models to Implementation

  6. Transformations CSCE 431 From Models to Implementation

  7. Model Transformation • Takes as input a model conforming to a meta model (for example the MOF metamodel) and produces as output another model conforming to the metamodel • Model transformations are used in MDA (Model Driven Architecture) CSCE 431 From Models to Implementation

  8. Model Transformation Example • Object design model before transformation: • Object design model after transformation: CSCE 431 From Models to Implementation

  9. Same Transformation in Code: Refactoring: Pull Up Field public class Player { private String email; //... } public class LeagueOwner { private String eMail; //... } public class Advertiser { private String email_address; //... } public class User { private String email; } public class Player extends User { //... } public class LeagueOwnerextends User { //... } public class Advertiser extends User { //... } CSCE 431 From Models to Implementation

  10. Refactoring Example: Pull Up Constructor Body public class User { private String email; } public class Player extends User { public Player(String email) { this.email= email; } } public class LeagueOwnerextends User{ public LeagueOwner(String email) { this.email= email; } } public class Advertiser extends User{ public Advertiser(String email) { this.email= email; } } public class User { public User(String email) { this.email= email; } } public class Player extends User { public Player(String email) { super(email); } } public class LeagueOwnerextends User { public LeagueOwner(String email) { super(email); } } public class Advertiser extends User { public Advertiser(String email) { super(email); } } CSCE 431 From Models to Implementation

  11. Refactoring • Refactorings cataloged the same was ay design patterns • http://refactoring.com/catalog/index.html • Many language IDEs offer powerful refactoring tools CSCE 431 From Models to Implementation

  12. Forward Engineering Example CSCE 431 From Models to Implementation

  13. More Forward Engineering Examples • Forward Engineering • Goal: Implementing the object design model in a programming language • Mapping inheritance • Mapping associations • Mapping contracts to exceptions • Mapping object models to tables CSCE 431 From Models to Implementation

  14. Reverse Engineering Example • Javadoc, Doxygen, … • Extract documentation from source code comments • Doxygen is open source, based on Oracle Javadoc • Roundtripengineering • MovebetweenaUMLviewandcodeatwill CSCE 431 From Models to Implementation

  15. Object Design Areas • Service specification • Describes precisely each class interface • Component selection • Identify off-the-shelf components and additional solution objects • Object model restructuring • Transforms the object design model to improve its understandability and extensibility • Object model optimization • Transforms the object design model to address performance criteria such as response time or memory utilization CSCE 431 From Models to Implementation

  16. Design Optimizations • Design optimizations are an important part of the object design phase: • The requirements analysis model is semantically correct but often too inefficient if directly implemented • Optimization activities during object design: • Add redundant associations to minimize access cost • What are the most frequent operations? ( Sensor data lookup?) • How often is the operation called? (30 times/mo, every 50 ms) • As an object designer you must strike a balance between efficiency and clarity • Optimizations will make your models more obscure CSCE 431 From Models to Implementation

  17. Object Design Optimizations (cont.) • Store derived attributes • Example: Define new classes to store information locally (database cache, proxy pattern) • Problem with derived attributes: • Derived attributes must be updated when base values change • 3 ways to deal with the update problem: • Explicit code: Implementer determines affected derived attributes (push) • Periodic computation: Recompute derived attribute occasionally (pull) • Active value: An attribute can designate set of dependent values which are automatically updated when the active value is changed (observer pattern, data trigger) CSCE 431 From Models to Implementation

  18. Model Transformations for Efficiency - Examples • Optimizing access paths • Possibly include redundant access paths • From “many” to “one” association through qualifications • Re-position attributes • Fold “uninteresting” attributes to calling class • Collapse objects (turn into attributes) • Delay expensive computations • Cache computation results CSCE 431 From Models to Implementation

  19. Collapsing Objects • Object design model before transformation: • Object design model after transformation: • Turning an object into an attribute of another object is usually done if the object does not have any interesting dynamic behavior (only get/set operations) CSCE 431 From Models to Implementation

  20. Delaying Expensive Operations • Object design model before transformation: • Object design model after transformation: Proxy Pattern CSCE 431 From Models to Implementation

  21. Forward Engineering: Mapping UML Model to Source Code • Goal: Translate UML-Model with inheritance - want to translate it into source code • Solution space: E.g. Java provides following mechanisms: • Overwriting of methods (default in Java) • Final classes • Final methods • Abstract methods • Abstract classes • Interfaces CSCE 431 From Models to Implementation

  22. Mapping Associations • Unidirectional one-to-one association • Bidirectional one-to-one association • Bidirectional one-to-many association • Bidirectional many-to-many association • Bidirectional qualified association CSCE 431 From Models to Implementation

  23. Unidirectional 1:1 Association CSCE 431 From Models to Implementation

  24. Bidirectional 1:1 Association CSCE 431 From Models to Implementation

  25. Bidirectional 1:N Association CSCE 431 From Models to Implementation

  26. Bidirectional N:N Association CSCE 431 From Models to Implementation

  27. Bidirectional Qualified Association CSCE 431 From Models to Implementation

  28. Bidirectional Qualified Association (2) CSCE 431 From Models to Implementation

  29. Summary: Implementing Associations • Strategy for implementing associations: • Be as uniform as possible • Individual decision for each association • Example of uniform implementation • 1:1 association: • Role names are treated like attributes in the classes and translate to references • 1:N association: • “Ordered many” : Translate to Vector • “Unordered many” : Translate to Set • Qualified association: • Translate to Hash table CSCE 431 From Models to Implementation

  30. Model-Driven Engineering (MDE) • http://en.wikipedia.org/wiki/Model_Driven_Engineering • MDE refers to a range of development approaches based on the use of SW modeling as a primary form of expression. Sometimes models are constructed to a certain level of detail, and then code is written by hand in a separate step. • Sometimes complete models are built including executable actions. Code can be generated from the models, ranging from system skeletons to complete, deployable products. • With the introduction of UML, MDE has become very popular today with a wide body of practitioners and supporting tools. More advanced types of MDE have expanded to permit industry standards which allow for consistent application and results. The continued evolution of MDE has added an increased focus on architecture and automation. • MDE technologies with a greater focus on architecture and corresponding automation yield higher levels of abstraction in SW development. This abstraction promotes simpler models with a greater focus on problem space. Combined with executable semantics this elevates the total level of automation possible. • OMG has developed a set of standards called model-driven architecture (MDA), building a foundation for this advanced architecture-focused approach. CSCE 431 From Models to Implementation

  31. MDE Historical View • First tools to support MDE were Computer-Aided Software Engineering (CASE) tools developed in 1980s • Companies like Integrated Development Environments (IDE - StP), Higher Order Software (now Hamilton Technologies, Inc., HTI), Cadre Technologies, Bachman Information Systems, and Logicworks (BP-Win and ER-Win) were pioneers • The government got involved in the modeling definitions creating the IDEF specifications. • New modeling languages (Booch, Rumbaugh, Jacobson, Ganes, Sarson, Harel, Shlaer, Mellor, others) led to Unified Modeling Language (UML) • Rational Rose was first dominant UML product, from Rational, now IBM • CASE had same problem that current MDA/MDE tools have today: model gets out of sync with source code CSCE 431 From Models to Implementation

  32. Terminology Review • Roundtrip Engineering • Forward Engineering + reverse engineering • Inventory Analysis: determine  between object model and code • Together-J, Rationale,… provide tools for reverse engineering • Reengineering • Used in context of project management: • Providing new functionality (additional customer needs) in context of new technology (technology enablers) CSCE 431 From Models to Implementation

  33. Implementing Contract Violations • Many OO languages do not have built-in support for contracts • Can use their exception mechanisms for signaling and handling contract violations • In Java we use the try-throw-catch mechanism • Example: • Assume acceptPlayer() operation of TournamentControlis invoked with a player who is already part of the Tournament • In this case acceptPlayer() in TournamentControlshould throw an exception of type KnownPlayer CSCE 431 From Models to Implementation

  34. Implementing a Contract • Check each pre-condition: • Check the pre-condition at beginning of method • Raise an exception if the pre-condition is false • Check each post-condition: • Check post-condition at end of method • Raise an exception if the post-condition is false. If more than one post-condition is false, raise an exception only for the first violation • Check each invariant: • Check invariants when checking pre- and post-conditions • Deal with inheritance: • Add the checking code for pre- and post-conditions into methods that can be called from the class CSCE 431 From Models to Implementation

  35. Mapping Contracts to Exceptions • Checking code slows down your program • If too slow, omit the checking code for private and protected methods • If still too slow, focus on components with the longest life • Omit checking code for post-conditions and invariants for all other components CSCE 431 From Models to Implementation

  36. Outline • From Object Model to Code • Mapping models to code • Operations on the object model: • Optimizations to address performance requirements • Implementation of class model components • Realization of associations • Realization of operation contracts • From Object Model to Persistent Data • Summary CSCE 431 From Models to Implementation

  37. From Models to Persistent Data • Random complaint from somewhere: • “UML Overemphasizes programming jargon, ignores databases” • However, UML models can also be used for generating a schema for a relational database • Schema derivable from class diagrams • Relational database only has a single entity type: table • Some of UML class diagrams’ richer structure lost • Tools offer automation (to both directions) CSCE 431 From Models to Implementation

  38. From Class Diagrams to Tables • Basics of the mapping • class mapped to a table • class attribute mapped to a column of a table • instance of a class is a row of a table • 1:1 association mapped to a foreign key • or two classes coalesced to one table • 1:N association mapped to a foreign key • N:N association mapped to a table of its own • No counterpart for methods • Object identity implicitly serves as a unique “key” in UML class diagrams • It may be necessary to add an explicit identity attribute to a table corresponding to a class CSCE 431 From Models to Implementation

  39. Example: Class to Table • This table might be OK w/o an ID attribute • Name seldom changes • OTOH, refs from other tables need to use the (relatively long) NAME • Decisions on representing data must be made • Constraints in the model, and eventually code, need to be updated to reflect the decisions CSCE 431 From Models to Implementation

  40. Why Unique ID is a Good Idea • Springfield Township, Bradford County, PA • Springfield Township, Bucks County, PA • Springfield Township, Delaware County, PA • Springfield Township, Erie County, PA • Springfield Township, Fayette County, PA • Springfield Township, Huntingdon County, PA • Springfield Township, Mercer County, PA • Springfield Township, Montgomery County, PA • Springfield Township, York County, PA CSCE 431 From Models to Implementation

  41. Data Representation • 2 char for state is okay in US • What about county name (see previous slide)? • Is 30 char okay for city name? • Rolling Hills Estates, CA – 21 char • Rancho Palos Verdes, CA – 19 char • Truth or Consequences NM – 19 char • Washington-on-the-Brazos, TX – 24 char • Winchester-on-the-Severn, MD – 24 char • Slovenska Narodna Podporna Jednota, PA – 34 char • Kinney and Gourlays Improved City Plat, UT – 38 char • “El Pueblo de Nuestra Señora la Reina de los Ángeles de la Porciúncula” LA – 68 char + accents • Might be 1781 name of LA • 40 charactersissafer, butlot of wastedspace • Intforpopulation? • 32-bit intisplentyforhumans and pets CSCE 431 From Models to Implementation

  42. 1:N Association • Is it really a 1:N association? • Implemented as foreign key CSCE 431 From Models to Implementation

  43. Reminder: Keys Candidate Key Aset of attributes that uniquely identifies a row of a table Primary Key One of the candidate keys selected to be used as the key of the table Foreign Key Set of attributes that references the primary key of another table CSCE 431 From Models to Implementation

  44. Example: Keys Problem! Al Jumahiriyah al Arabiyah al Libiyah ash Shabiyah al Ishtirakiyah al Uzma CSCE 431 From Models to Implementation

  45. Example: 1:N Probably okay 32-bit INT marginal CSCE 431 From Models to Implementation

  46. 1:1 Associations CSCE 431 From Models to Implementation

  47. Foreign Key Can be Placed in Either Table CSCE 431 From Models to Implementation

  48. Navigation • Previous tables corresponded to diagram on left • (Fast) navigability in both directions may require indices CSCE 431 From Models to Implementation

  49. 1:1: Possible to Represent as One Table CSCE 431 From Models to Implementation

  50. N:N Associations Too short w/ “International Airport” in name CSCE 431 From Models to Implementation

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