System requirements

Functional:

List functional requirements for the system (Ask interviewer if stuck)...

1. Users are able to add/delete/update tags
2. Tags should support different data types
3. Support search, filter
4. Support tags recommendation (optional)
5. Support tags normalization

Non-Functional:

List non-functional requirements for the system...

1. Highly available
2. easy to scale
3. ensure efficient fast retrieval and search

Capacity estimation

Estimate the scale of the system you are going to design...

Assume that there are 10,000 DAU, each user has 500 tags on average. So there are 500*10,000 = 5,000,000 tags in total

Assume that each user add 5 tags per day, then there are 50,000 tags added per day

if 20% of the datas added per day are updated, then 50,000 * 20% = 10,000 updates per day;

Assume each tag is 80 bytes, then we need at least 5,000,000 * 80 bytes = 0.4 Gb

API design

Define what APIs are expected from the system...

RESTful APIs:

@Create

void create(String tagName)

@Batch_Create

void batchCreate(List tagNames)

@Update

void update(Tag tag)

@Delete

void delete(Tag tag)

@Get

List getTags()

List recommendTags(String input)

List normalizeTags(List tags)

List searchByTags(List tags)

Database design

Defining the system data model early on will clarify how data will flow among different components of the system. Also you could draw an ER diagram using the diagramming tool to enhance your design...

Data model:

Tag {

id: int (autoincrement),

name: varchar,

metadata: varchar

}

TagCategory {

id: int,

name: varchar,

}

TagToCategoryMapping {

tagId: int,

categoryId: int

}

Choice of Database:

1. Relational database (eg, postgreSQL)

High-level design

You should identify enough components that are needed to solve the actual problem from end to end. Also remember to draw a block diagram using the diagramming tool to augment your design...

Request flows

Explain how the request flows from end to end in your high level design. Also you could draw a sequence diagram using the diagramming tool to enhance your explanation...

Detailed component design

Dig deeper into 2-3 components and explain in detail how they work. For example, how well does each component scale? Any relevant algorithm or data structure you like to use for a component? Also you could draw a diagram using the diagramming tool to enhance your design...

Trade offs/Tech choices

Explain any trade offs you have made and why you made certain tech choices...

Failure scenarios/bottlenecks

Try to discuss as many failure scenarios/bottlenecks as possible.

Future improvements

What are some future improvements you would make? How would you mitigate the failure scenario(s) you described above?