Model-Driven Software Development - Web Abstractions 2

Web Abstractions 1Iaccess control policies, data validation, workflow, ajax, search

Course IN4308Master Computer Science

Delft University of Technology

Eelco Visserhttp://eelcovisser.org

Lecture 4

Wednesday, March 10, 2010

Modeling Software Systems

Modeling Web Programs

Implementing Web Models

Modeling Software Languages

Transforming Software Models

Make your own Software Languages

Modeling IDEs

Software Language Engineering Strategies


Web Abstractions

from a declarative point of view(we’ll investigate underlying mechanisms later)


More Web Abstractions

- Access control policies

★ constraints over objects

★ role-based AC, discretionary AC

- Data validation

★ form validation

★ data integrity

- Workflow

- Search

- AJAX: accessing page fragments (templates)


Access Control

Danny M. Groenewegen, Eelco Visser. Declarative Access Control for WebDSL: Combining Language Integration and Separation of Concerns. ICWE 2008: 175-188


http://researchr.org/profile/dannymgroenewegen/publications


http://researchr.org/profile/eelcovisser/publications


http://researchr.org/publication/GroenewegenV08




http://researchr.org/publication/icwe%3A2008

http://researchr.org/publication/icwe%3A2008

Case 2: Access Control Policy for Conference

Papers

★ has authors

Authors

★ submit papers, read reviews

Reviewers

★ write review for paper & discuss papers

★ are anonymous (for authors)

Conflicts

★ author cannot be reviewer

★ reviewer not related to authors


Access Control Mechanisms


WebDSL Access Control

Constraints over data model

- boolean expression over properties of objects

Rules restrict access to resources

- page, template, action

Infer restriction of navigation

- don’t show link to inaccessible page or forbidden action


Principal

turn on access control

representation of principal


Access Control Rules

‘may access page f with argument x if boolean expression e is true’


Wiki Access Control Rules

‘only logged in users may edit pages’

‘anyone can view existing pages, only logged in users can

create pages’


Wiki Access Control Rules


Access Control Policies


Access Control Policies

Standard Policies

- Mandatory access control

- Discretionary access control

- Role-based access control

Mixing policies

- Role-based + discretionary access control

WebDSL

- No restrictions on access control policies


Encoding Access Control Policies

Rules

- Who may access which resources?

- Who can apply which actions?

Representation

- How are permissions stored?

Administration

- How can permissions be changed?

- Who can change permissions?


Wiki: Data Model


Wiki: User Interface Templates

(abbreviated to navigation structure)Wednesday, March 10, 2010

Wiki: Generic Access Control Rules


Mandatory Access Control

Security Labels

★ Classification label protects object

• Top Secret, Secret, Confidential, Unclassified

★ Clearance indicates access of subject

Confidentiality rules

★ Read-down: clearance should be higher than or equal to classification document to read

★ Write-up: clearance is lower than or equal to classification of document to write


MAC: representation


MAC: predicates


Discretionary Access Control

Access control lists

- objects have owner

- owner grants, revokes users access to object

Example: Unix file permissions

- read, write, execute permissions for

- owner, group, anyone


DAC: representation


DAC: predicates


DAC: administration


Role-Based Access Control

Role: group of activities

- authorization assigned to roles

- users assigned to roles

- robust to organizational changes

Hierarchical roles

- least privilege: use minimal permissions for task

Separation of duties

- critical actions require coordination


RBAC: representation


RBAC: predicates


RBAC: administration


Mixing Access Control Policies

Real policies

- Mix of DAC & RBAC

- AC rules are constraints over object graph

WebDSL

- No policies built-in


Case 2: Access Control Policy for Conference

Papers

★ has authors

Authors

★ submit papers, read reviews

Reviewers

★ write review for paper & discuss papers

★ are anonymous (for authors)

Conflicts

★ author cannot be reviewer

★ reviewer not related to authors


Data Validation

Danny M. Groenewegen, Eelco Visser. Integration of Data Validation and User Interface Concerns in a DSL for Web Applications. SLE 2010






http://researchr.org/publication/GroenewegenV%3ASLE%3A2009




http://researchr.org/publication/sle%3A2009

http://researchr.org/publication/sle%3A2009

Data Validation

Check input & maintain data integrity

Types of validation

- Value well-formedness

- Data invariants

- Input assertions

- Action assertions

User interface integration

- Display errors


Validation Rules

data validation

form validation

action assertions messages


Value Well-Formedness


Customizing Value Well-Formedness Rules


Data Invariants


Input Assertions


Action Assertions


Customizing Error Messages


Workflow

Note: WebWorkFlow is not supported by current version of WebDSL

Zef Hemel, Ruben Verhaaf, Eelco Visser. WebWorkFlow: An Object-Oriented Workflow Modeling Language for Web Applications. MoDELS 2008: 113-127


http://researchr.org/profile/zefhemel/publications

http://researchr.org/profile/zefhemel/publications

http://researchr.org/profile/rubenverhaaf/publications

http://researchr.org/profile/rubenverhaaf/publications



http://researchr.org/publication/HemelVV08




http://researchr.org/publication/models%3A2008

http://researchr.org/publication/models%3A2008

Workflow

Coordinating activities by participants

WebWorkFlow

- object-oriented workflow definition

- integrate all aspects of workflow

★ data

★ user interface

★ access control

★ control-flow

- abstractions on top of base WebDSL


WebWorkFlow by Example: Progress Meeting


process definition

workflow procedureworkflow object

procedure call


enable next step

parallel

iterate


access control

access controlWednesday, March 10, 2010

action


no user interface


condition


Workflow Remarks

Recursive workflows (see paper)

Issue: user interface patterns for workflow

Is workflow an anti-pattern?

- is workflow good interaction design?

- determine order of user actions

- what are alternatives?


Search


search annotations

search queries


AJAX

Michel Weststrate. Abstractions for Asynchronous User Interfaces in Web Applications.Master's thesis, Delft University of Technology, 2009.


AJAX

Deliver page fragments, not just full pages

- Replace page elements by new fragments

- Templates are unit of replacement


placeholder

default view


replace


Summary

Access control policies

★ constraints over objects

★ encoding of standard policies (DAC, RBAC)

Data validation

★ form validation & data integrity

Workflow

★ coordinating activities of multiple participants

Search based on data model annotations

AJAX: accessing page fragments (templates)


Schedule

Lab this week

★ WebDSL application

Cases

★ Case 2: web abstractions

★ Read: Declarative Access Control for WebDSL

★ Read: Integration of Data Validation and User Interface Concerns

★ Read: WebWorkFlow

Next

★ Lecture 5: WebDSL implementation strategies

★ Lecture 6 & 7: modeling languagesWednesday, March 10, 2010

Model-Driven Software Development - Web Abstractions 2

Education

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