Product Perfect

VDM-SL (Vienna Development Method Specification Language) is a formal language used in software development for specifying and designing computer-based systems. It was developed at IBM's Vienna Laboratory in the 1970s and has been widely used for both industrial and academic purposes. VDM-SL supports a broad range of modeling concepts, allowing developers to define system requirements, behavior, and architecture precisely. It provides mechanisms for modeling data structures as well as operations on these structures with explicit state transition semantics. The use of VDM-SL can significantly improve the reliability of software by enabling rigorous specification, analysis, validation, verification and testing processes during the early stages of system development.

Ask the right questions secure the right VDM-SL talent among an increasingly shrinking pool of talent.

First 20 minutes

General VDM-SL app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in VDM-SL application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

What are the key features of VDM-SL?

The key features of VDM-SL include strong typing, state-based modeling, support for abstraction and refinement, and support for modularization.

How would you define a new data type in VDM-SL?

In VDM-SL, a new data type can be defined using the 'types' keyword followed by the data type name, the '=' symbol, and the data type definition.

What are the types of expressions in VDM-SL?

VDM-SL supports several types of expressions including arithmetic expressions, boolean expressions, set expressions, sequence expressions, and map expressions.

How would you define a state in VDM-SL?

A state in VDM-SL can be defined using the 'state' keyword followed by the state name, the 'of' keyword, and the state variables.

Describe the difference between 'let' and 'let be st' in VDM-SL.

'Let' is used to define local variables in an expression, while 'let be st' is used to define a non-deterministic choice.

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What you’re looking for early on

Does the candidate demonstrate a clear understanding of VDM-SL (Vienna Development Method Specification Language)?

Has the candidate been able to provide examples of previous projects where they've successfully used VDM-SL?

Does the candidate show problem-solving skills and the ability to think logically?

How well does the candidate understand formal methods and their role in software development?

Next 20 minutes

Specific VDM-SL development questions

The next 20 minutes of the interview should focus on the candidate's expertise with specific backend frameworks, their understanding of RESTful APIs, and their experience in handling data storage and retrieval efficiently.

How would you define a function in VDM-SL?

A function in VDM-SL can be defined using the 'functions' keyword followed by the function name, the function parameters, the ':' symbol, the return type, and the function body.

What are the types of invariants in VDM-SL?

VDM-SL supports two types of invariants: type invariants and state invariants.

Describe the difference between 'pre' and 'post' in VDM-SL.

'Pre' is used to define a precondition for a function or operation, while 'post' is used to define a postcondition.

How would you define an operation in VDM-SL?

An operation in VDM-SL can be defined using the 'operations' keyword followed by the operation name, the operation parameters, the ':' symbol, the return type, and the operation body.

What are the types of patterns in VDM-SL?

VDM-SL supports several types of patterns including match value patterns, identifier patterns, match type patterns, and tuple patterns.

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At this point, a skilled VDM-SL engineer should demonstrate strong problem-solving abilities, proficiency in VDM-SL programming language, and knowledge of software development methodologies. Red flags include lack of hands-on experience, inability to articulate complex concepts, or unfamiliarity with standard coding practices.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with VDM-SL.

What does this simple VDM-SL code do?
values
  pi = 3.14159
This code defines a value named 'pi' and assigns the floating point number 3.14159 to it.
What does this VDM-SL code do?
types
  DayOfWeek =  |  |  |  |  |  | 
This code defines a new type 'DayOfWeek' which can be one of the seven days of the week.
What will be the output of this VDM-SL code?
functions
  sum: seq of nat -> nat
  sum(s) == if s = [] then 0 else hd s + sum(tl s)
This code defines a recursive function 'sum' that takes a sequence of natural numbers as input and returns their sum. If the sequence is empty, it returns 0.
What does this VDM-SL code do?
operations
  startThread: () ==> ()
  startThread() == skip;

  stopThread: () ==> ()
  stopThread() == skip;
This code defines two operations 'startThread' and 'stopThread' that do nothing ('skip'). These could be placeholders for real thread start and stop operations.

Wrap-up questions

Final candidate for VDM-SL Developer role questions

The final few questions should evaluate the candidate's teamwork, communication, and problem-solving skills. Additionally, assess their knowledge of microservices architecture, serverless computing, and how they handle VDM-SL application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

Describe the difference between 'cases' and 'if-then-else' in VDM-SL.

'Cases' is used for multi-way selection based on pattern matching, while 'if-then-else' is used for two-way selection based on a boolean condition.

How would you define a module in VDM-SL?

A module in VDM-SL can be defined using the 'module' keyword followed by the module name, the 'exports' keyword, the exported items, the 'imports' keyword, and the imported items.

What are the types of definitions in VDM-SL?

VDM-SL supports several types of definitions including type definitions, value definitions, function definitions, operation definitions, and state definitions.

VDM-SL application related

Product Perfect's VDM-SL development capabilities

Beyond hiring for your VDM-SL engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in VDM-SL projects, and can engage in multiple capacities.

VDM-SL Consultive assessments

VDM-SL Application Conversion Assessment VDM-SL Application Integration Assessment VDM-SL Data & Database Integration Assessment

Custom VDM-SL development projects

Custom VDM-SL App Conversion VDM-SL Custom App Development Process App UI Design for VDM-SL Facelifts

Hiring guide for VDM-SL Engineers

VDM-SL Developer Hiring Guide

What you’re looking for early on

The ideal back-end app developer

What you’re looking to see on the VDM-SL engineer at this point.

VDM-SL Consultive assessments

Custom VDM-SL development projects