了解的运作原理之后，就可以开始使用Semantic Kernel来制作应用了。
Semantic Kernel将embedding的功能封装到了Memory中，用来存储上下文信息，就好像电脑的内存一样，而LLM就像是CPU一样，我们所需要做的就是从内存中取出相关的信息交给CPU处理就好了。
内存配置
使用Memory需要注册 embedding模型，目前使用的就是 text-embedding-ada-002。同时需要为Kernel添加MemoryStore，用于存储更多的信息，这里Semantic Kernel提供了一个 VolatileMemoryStore，就是一个普通的内存存储的MemoryStore。
var kernel = Kernel.Builder.Configure(c =>
{
c.AddOpenAITextCompletionService("openai", "text-davinci-003", Environment.GetEnvironmentVariable("MY_OPEN_AI_API_KEY"));
c.AddOpenAIEmbeddingGenerationService("openai", "text-embedding-ada-002", Environment.GetEnvironmentVariable("MY_OPEN_AI_API_KEY"));
})
.WithMemoryStorage(new VolatileMemoryStore())
.Build();
信息存储
完成了基础信息的注册后，就可以往Memroy中存储信息了。
const string MemoryCollectionName = "aboutMe";
await kernel.Memory.SaveInformationAsync(MemoryCollectionName, id: "info1", text: "My name is Andrea");
await kernel.Memory.SaveInformationAsync(MemoryCollectionName, id: "info2", text: "I currently work as a tourist operator");
await kernel.Memory.SaveInformationAsync(MemoryCollectionName, id: "info3", text: "I currently live in Seattle and have been living there since 2005");
await kernel.Memory.SaveInformationAsync(MemoryCollectionName, id: "info4", text: "I visited France and Italy five times since 2015");
await kernel.Memory.SaveInformationAsync(MemoryCollectionName, id: "info5", text: "My family is from New York");
SaveInformationAsync 会将text的内容通过 embedding 模型转化为对应的文本向量，存放在的MemoryStore中。其中CollectionName如同数据库的表名，Id就是Id。
语义搜索
完成信息的存储之后，就可以用来语义搜索了。
直接使用Memory.SearchAsync方法，指定对应的Collection，同时提供相应的查询问题，查询问题也会被转化为embedding，再在MemoryStore中计算查找最相似的信息。
var questions = new[]
{
"what is my name?",
"where do I live?",
"where is my family from?",
"where have I travelled?",
"what do I do for work?",
};
foreach (var q in questions)
{
var response = await kernel.Memory.SearchAsync(MemoryCollectionName, q).FirstOrDefaultAsync();
Console.WriteLine(q + " " + response?.Metadata.Text);
}
// output
/*
what is my name? My name is Andrea
where do I live? I currently live in Seattle and have been living there since 2005
where is my family from? My family is from New York
where have I travelled? I visited France and Italy five times since 2015
what do I do for work? I currently work as a tourist operator
*/
到这个时候，即便不需要进行总结归纳，光是这样的语义查找，都会很有价值。
引用存储
除了添加信息以外，还可以添加引用，像是非常有用的参考链接之类的。
const string memoryCollectionName = "SKGitHub";
var githubFiles = new Dictionary<string, string>()
{
["https://github.com/microsoft/semantic-kernel/blob/main/README.md"]
= "README: Installation, getting started, and how to contribute",
["https://github.com/microsoft/semantic-kernel/blob/main/samples/notebooks/dotnet/2-running-prompts-from-file.ipynb"]
= "Jupyter notebook describing how to pass prompts from a file to a semantic skill or function",
["https://github.com/microsoft/semantic-kernel/blob/main/samples/notebooks/dotnet/Getting-Started-Notebook.ipynb"]
= "Jupyter notebook describing how to get started with the Semantic Kernel",
["https://github.com/microsoft/semantic-kernel/tree/main/samples/skills/ChatSkill/ChatGPT"]
= "Sample demonstrating how to create a chat skill interfacing with ChatGPT",
["https://github.com/microsoft/semantic-kernel/blob/main/dotnet/src/SemanticKernel/Memory/Volatile/VolatileMemoryStore.cs"]
= "C# class that defines a volatile embedding store",
["https://github.com/microsoft/semantic-kernel/tree/main/samples/dotnet/KernelHttpServer/README.md"]
= "README: How to set up a Semantic Kernel Service API using Azure Function Runtime v4",
["https://github.com/microsoft/semantic-kernel/tree/main/samples/apps/chat-summary-webapp-react/README.md"]
= "README: README associated with a sample starter react-based chat summary webapp",
};
foreach (var entry in githubFiles)
{
await kernel.Memory.SaveReferenceAsync(
collection: memoryCollectionName,
description: entry.Value,
text: entry.Value,
externalId: entry.Key,
externalSourceName: "GitHub"
);
}
同样的，使用SearchAsync搜索就行。
string ask = "I love Jupyter notebooks, how should I get started?";
Console.WriteLine("===========================\n" +
"Query: " + ask + "\n");
var memories = kernel.Memory.SearchAsync(memoryCollectionName, ask, limit: 5, minRelevanceScore: 0.77);
var i = 0;
await foreach (MemoryQueryResult memory in memories)
{
Console.WriteLine($"Result {++i}:");
Console.WriteLine(" URL: : " + memory.Metadata.Id);
Console.WriteLine(" Title : " + memory.Metadata.Description);
Console.WriteLine(" ExternalSource: " + memory.Metadata.ExternalSourceName);
Console.WriteLine(" Relevance: " + memory.Relevance);
Console.WriteLine();
}
//output
/*
===========================
Query: I love Jupyter notebooks, how should I get started?
Result 1:
URL: : https://github.com/microsoft/semantic-kernel/blob/main/samples/notebooks/dotnet/Getting-Started-Notebook.ipynb
Title : Jupyter notebook describing how to get started with the Semantic Kernel
ExternalSource: GitHub
Relevance: 0.8677381632778319
Result 2:
URL: : https://github.com/microsoft/semantic-kernel/blob/main/samples/notebooks/dotnet/2-running-prompts-from-file.ipynb
Title : Jupyter notebook describing how to pass prompts from a file to a semantic skill or function
ExternalSource: GitHub
Relevance: 0.8162989178955157
Result 3:
URL: : https://github.com/microsoft/semantic-kernel/blob/main/README.md
Title : README: Installation, getting started, and how to contribute
ExternalSource: GitHub
Relevance: 0.8083238591883483
*/
这里多使用了两个参数，一个是limit，用于限制返回信息的条数,只返回最相似的前几条数据，另外一个是minRelevanceScore，限制最小的相关度分数，这个取值范围在0.0 ~ 1.0 之间，1.0意味着完全匹配。
语义问答
将Memory的存储、搜索功能和语义技能相结合，就可以快速的打造一个实用的语义问答的应用了。
只需要将搜索到的相关信息内容填充到 prompt中，然后将内容和问题都抛给LLM，就可以等着得到一个满意的答案了。
const string MemoryCollectionName = "aboutMe";
await kernel.Memory.SaveInformationAsync(MemoryCollectionName, id: "info1", text: "My name is Andrea");
await kernel.Memory.SaveInformationAsync(MemoryCollectionName, id: "info2", text: "I currently work as a tourist operator");
await kernel.Memory.SaveInformationAsync(MemoryCollectionName, id: "info3", text: "I currently live in Seattle and have been living there since 2005");
await kernel.Memory.SaveInformationAsync(MemoryCollectionName, id: "info4", text: "I visited France and Italy five times since 2015");
await kernel.Memory.SaveInformationAsync(MemoryCollectionName, id: "info5", text: "My family is from New York");
var prompt =
"""
It can give explicit instructions or say 'I don't know' if it does not have an answer.
Information about me, from previous conversations:
{{ $fact }}
User: {{ $ask }}
ChatBot:
""";
var skill = kernel.CreateSemanticFunction(prompt);
var ask = "Hello, I think we've met before, remember? my name is...";
var fact = await kernel.Memory.SearchAsync(MemoryCollectionName,ask).FirstOrDefaultAsync();
var context = kernel.CreateNewContext();
context["fact"] = fact?.Metadata?.Text;
context["ask"] = ask;
var resultContext =await skill.InvokeAsync(context);
resultContext.Result.Dump();
//output
/*
Hi there! Yes, I remember you. Your name is Andrea, right?
*/
优化搜索过程
由于这种场景太常见了，所以Semantic Kernel中直接提供了一个技能TextMemorySkill，通过Function调用的方式简化了搜索的过程。
// .. SaveInformations
// TextMemorySkill provides the "recall" function
kernel.ImportSkill(new TextMemorySkill());
var prompt =
"""
It can give explicit instructions or say 'I don't know' if it does not have an answer.
Information about me, from previous conversations:
{{ recall $ask }}
User: {{ $ask }}
ChatBot:
""";
var skill = kernel.CreateSemanticFunction(prompt);
var ask = "Hello, I think we've met before, remember? my name is...";
var context = kernel.CreateNewContext();
context["ask"] = ask;
context[TextMemorySkill.CollectionParam] = MemoryCollectionName;
var resultContext =await skill.InvokeAsync(context);
resultContext.Result.Dump();
// output
/*
Hi there! Yes, I remember you. Your name is Andrea, right?
*/
这里直接使用 recall 方法，将问题传给了 TextMemorySkill，搜索对应得到结果，免去了手动搜索注入得过程。
内存的持久化
VolatileMemoryStore本身也是易丢失的，往往使用到内存的场景，其中的信息都是有可能长期存储的，起码并不会即刻过期。那么将这些信息的 embedding 能够长期存储起来，也是比较划算的事情。毕竟每一次做 embedding的转化也是需要调接口，需要花钱的。
Semantic Kernel库中包含了SQLite、Qdrant和CosmosDB的实现，自行扩展的话，也只需要实现 IMemoryStore 这个接口就可以了。
至于未来，可能就是专用的 Vector Database 了。
参考资料：
- https://learn.microsoft.com/en-us/semantic-kernel/concepts-sk/memories
- https://github.com/microsoft/semantic-kernel/blob/main/samples/notebooks/dotnet/6-memory-and-embeddings.ipynb
- https://github.com/johnmaeda/SK-Recipes/blob/main/e4-memories/notebook.ipynb
- https://learn.microsoft.com/en-us/semantic-kernel/concepts-ai/vectordb