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

Wednesday, March 10, 2010

Web Abstractions

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

Wednesday, March 10, 2010

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)

Wednesday, March 10, 2010

Access Control

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

Wednesday, March 10, 2010

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

Wednesday, March 10, 2010

Access Control Mechanisms

Wednesday, March 10, 2010

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

Wednesday, March 10, 2010

Principal

turn on access control

representation of principal

Wednesday, March 10, 2010

Access Control Rules

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

Wednesday, March 10, 2010

Wiki Access Control Rules

‘only logged in users may edit pages’

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

create pages’

Wednesday, March 10, 2010

Wiki Access Control Rules

Wednesday, March 10, 2010

Wiki Access Control Rules

Wednesday, March 10, 2010

Wiki Access Control Rules

Wednesday, March 10, 2010

Wiki Access Control Rules

Wednesday, March 10, 2010

Access Control Policies

Wednesday, March 10, 2010

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

Wednesday, March 10, 2010

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?

Wednesday, March 10, 2010

Wiki: Data Model

Wednesday, March 10, 2010

Wiki: User Interface Templates

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

Wiki: Generic Access Control Rules

Wednesday, March 10, 2010

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

Wednesday, March 10, 2010

MAC: representation

Wednesday, March 10, 2010

MAC: predicates

Wednesday, March 10, 2010

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

Wednesday, March 10, 2010

DAC: representation

Wednesday, March 10, 2010

DAC: predicates

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DAC: administration

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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

Wednesday, March 10, 2010

RBAC: representation

Wednesday, March 10, 2010

RBAC: predicates

Wednesday, March 10, 2010

RBAC: administration

Wednesday, March 10, 2010

Mixing Access Control Policies

Real policies

- Mix of DAC & RBAC

- AC rules are constraints over object graph

WebDSL

- No policies built-in

Wednesday, March 10, 2010

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

Wednesday, March 10, 2010

Data Validation

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

Wednesday, March 10, 2010

Data Validation

Check input & maintain data integrity

Types of validation

- Value well-formedness

- Data invariants

- Input assertions

- Action assertions

User interface integration

- Display errors

Wednesday, March 10, 2010

Validation Rules

data validation

form validation

action assertions messages

Wednesday, March 10, 2010

Value Well-Formedness

Wednesday, March 10, 2010

Customizing Value Well-Formedness Rules

Wednesday, March 10, 2010

Data Invariants

Wednesday, March 10, 2010

Data Invariants

Wednesday, March 10, 2010

Data Invariants

Wednesday, March 10, 2010

Data Invariants

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Input Assertions

Wednesday, March 10, 2010

Action Assertions

Wednesday, March 10, 2010

Customizing Error Messages

Wednesday, March 10, 2010

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

Wednesday, March 10, 2010

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

Wednesday, March 10, 2010

WebWorkFlow by Example: Progress Meeting

Wednesday, March 10, 2010

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process definition

workflow procedureworkflow object

procedure call

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enable next step

parallel

iterate

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access control

access controlWednesday, March 10, 2010

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action

Wednesday, March 10, 2010

no user interface

Wednesday, March 10, 2010

condition

Wednesday, March 10, 2010

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?

Wednesday, March 10, 2010

Search

Wednesday, March 10, 2010

search annotations

search queries

Wednesday, March 10, 2010

AJAX

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

Wednesday, March 10, 2010

AJAX

Deliver page fragments, not just full pages

- Replace page elements by new fragments

- Templates are unit of replacement

Wednesday, March 10, 2010

placeholder

default view

Wednesday, March 10, 2010

replace

Wednesday, March 10, 2010

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)

Wednesday, March 10, 2010

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