How do we map data flow into a software architecture?

In architectural design, the mapping method uses data flow characteristics to derive a commonly used architectural style. A data flow diagram is mapped into program structure using one of the two mapping approaches:
- Transform Mapping
- Transaction Mapping
Structured design is often characterized as a data flow oriented design method because it provides a convenient transition from a data flow diagram. This type of information flow is the driver for the mapping approach.
Transform Flow: The overall flow of data occurs in a sequential manner and follows one, or only a few straight line paths. When a segment of a data flow diagram exhibits these characteristics, transform flow is present.

Transaction Flow: Information flow which is characterized by single data item called a transaction that triggers other data flow along one of many paths. When a data flow diagram takes this kind of form then transaction flow is present.

TRANSFORM MAPPING

It is a set of design steps that allows a data flow diagram with transform flow characteristics to be mapped into a specific architectural style.
- Review the fundamental system model.
- Review and refine data flow diagrams for the software.
- Determine whether the data flow diagram has transform or transaction flow characteristics.
- Isolate the transform center by specifying incoming and outgoing flow boundaries.
- Perform first level factoring.
- Perform second level factoring.
- Refine the first iteration architecture using design heuristics for improved software quality.

TRANSACTION MAPPING

In transaction mapping, information flow along two of the three action paths accommodates additional incoming flow. Each action path flows into a single transform, display messages and status. The design steps for transaction mapping is similar with a major difference lies in mapping of data flow diagram to software structure.
- Review the fundamental system model.
- Review and refine data flow diagrams for the software.
- Determine whether the data flow diagram has transform or transaction flow characteristics.
- Identify the transaction center and the flow characteristics along each of the action paths.
- Map the data flow diagram in a program structure amenable to transaction processing.
- Factor and refine the transaction structure and the structure of each action path.
- Refine the first iteration architecture using design heuristics for improved software quality.

Once an architecture has been derived, it is elaborated and then analyzed against quality criteria.

What are different tasks representing WebApp interface design?

The user interface design begins with
- identification of user.
- identification of task.
- identification of environmental requirements.
Once these are identified, user scenarios are created and analyzed.

TASKS REPRESENTING WEB APPLICATION INTERFACE DESIGN ARE:

- The information that is contained in the analysis model is reviewed and refined as required.
- A rough sketch of web application interface layout is developed.
- The user objectives should be mapped into specific interface actions.
- A set of user tasks associated with action should be defined.
- Each interface action should have a storyboard screen image which depicts the interface response to user interaction.
- The input from aesthetic design should be used to refine the interface layout and storyboards.
- Implementing interface requires user interface objects. These user interface objects should be identified which may require a search through an existing object library.
- A procedural representation of user's interaction with interface is developed.
- A behavioral representation of the interface is also developed. It may use UML state diagrams to represent state mechanisms.
- Each state's interface layout is described using design information developed in tasks 2 and tasks 5.
- The interface design model should be refined and reviewed.

Implementation techniques and Remote File Access for Distributed File Systems

Implementation of transparent naming requires a provision for the mapping of a file name to the associated location. Keeping this mapping manageable calls for aggregating sets of files into component units, and providing the mapping on a component unit basis rather than on a single file basis. To enhance the availability of the crucial mapping information, methods like replication, local caching, or both can be used.
A non-transparent mapping technique:
name ----> < system, disk, cylinder, sector >
A transparent mapping technique:
name ----> file_identifier ----> < system, disk, cylinder, sector >
So, when changing the physical location of a file, only the file identifier need be modified. This identifier must be "unique" in the universe.

Remote File Access
In remote-service mechanism, requests for accesses are delivered to the server, the server machine performs the accesses, and their results are forwarded back to the user. The remote-service method is analogous to performing a disk access for each access request. To ensure reasonable performance of a remote-service mechanism, caching is used. In DFSs, the goal is to reduce both network traffic and disk I/O.

Secondary Storage Structure - Disk Structure

Secondary storage structure helps to :
- Describe the physical structure of secondary and tertiary storage devices and the resulting effects on the uses of the devices.
- Explain the performance characteristics of mass-storage devices.
- Discuss operating-system services provided for mass storage, including RAID and HSM.

Disk provide the bulk of secondary storage for modern computer systems. Disk drives are addressed as large 1-dimensional arrays of logical blocks, where the logical block is the smallest unit of transfer. The 1-dimensional array of logical blocks is mapped onto the sectors of the disk sequentially.
- Sector 0 is the first sector of the first track on the outermost cylinder.
- Mapping proceeds in order through that track, then the rest of the tracks in that cylinder, and then through the rest of the cylinders from outermost to innermost.
- The operating system is responsible for using hardware efficiently — for the disk drives, this means having a fast access time and disk bandwidth.
- Access time has two major components.
* Seek time is the time for the disk arm to move the heads to the cylinder containing the desired sector.
* Rotational latency is the additional time waiting for the disk to rotate the desired sector to the disk head.
- Minimize seek time.
- Seek time seek distance.
- Disk bandwidth is the total number of bytes transferred, divided by the total time between the first request for service and the completion of the last transfer.
- Several algorithms exist to schedule the servicing of disk I/O requests.